Wikipedia:Manual of Style (dates and numbers)

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"WP:DATE" redirects here. For the other guideline, see Wikipedia:Avoid statements that will date quickly.
✔ This guideline is a part of the English Wikipedia's Manual of Style. Editors should follow it, except where common sense and the occasional exception will improve an article. Before editing this page, please make sure that your revision reflects consensus.
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This part of the Manual of Style aims to achieve consistency in the use and formatting of dates and numbers in Wikipedia articles. Consistent standards make articles easier to read, write and edit. Where this manual provides options, consistency should be maintained within an article, unless there is a good reason to do otherwise. In direct quotations, the original text should be preserved.

In June 2005, the Arbitration Committee ruled that when either of two styles such as 14 February or February 14 is acceptable, it is inappropriate for an editor to change an article from one style to another unless there is a substantial reason to do so. Edit warring over optional styles is unacceptable. If an article has been stable in a given style, it should not be converted without a style-independent reason. Where in doubt, defer to the style used by the first major contributor.

Contents

Non-breaking spaces

Shortcut:
WP:NBSP
See also: Wikipedia:Line break handling and Wikipedia:Manual of Style#Non-breaking spaces
  • A non-breaking space (also known as a hard space) is recommended to avoid the end-of-line displacement of the elements:
    • in compound expressions in which figures and abbreviations or symbols are separated by a space (17 kg, AD 565, 2:50 pm);
    • between month and day in dates that are not autoformatted (August 3, 1979);
    • on the left side of spaced en dashes; and
    • in other places where displacement might be disruptive to the reader, such as £11 billion, 5° 24′ 21.12″ N, Boeing 747, and the first two items in 7 World Trade Center.
  • A hard space can be produced with the HTML code   instead of the space bar, or by pressing the key combination option–space bar on a Mac: 19 kg yields a non-breaking 19 kg.
  • Hard spaces can also be produced by using the {{nowrap}} template: {{nowrap|8 sq ft}} produces a non-breaking 8 sq ft. This is especially useful for short constructions requiring two or more hard spaces, as in the preceding example. Template {{nowrap}} has the disadvantage that if the enclosed text starts or ends with a space, these spaces are forced outside in the resulting HTML, and unpredicted breaks may occur. If   occurs right before {{nowrap}}, or at the start of text within {{nowrap}}, some browsers allow a break at that point.
  • In some older browsers, quotation marks separated by a hard space are broken at the end of a line: ("She said 'Yes!' ").
  • Unlike normal spaces, multiple hard spaces are not compressed by browsers into a single space.

Chronological items

Precise language

Avoid statements that will date quickly, except on pages that are regularly updated, such as those that cover current events. Avoid such items as recently and soon (unless their meaning is clear in a storyline), currently (except on rare occasions when it is not redundant), and is soon to be superseded. Instead, use either:

  • more precise items (since the start of 2005; during the 1990s; is expected to be superseded by 2008); or
  • an as of phrase (as of August 2007), which is a signal to readers of the time-dependence of the statement, and to later editors of the need to update the statement (see As of).

Times

Context determines whether the 12- or 24-hour clock is used; in both, colons separate hours, minutes and seconds (1:38:09 pm and 13:38:09).

  • 12-hour clock times end with dotted or undotted lower-case a.m. or p.m., or am or pm, which are spaced (2:30 p.m. or 2:30 pm, not 2:30p.m. or 2:30pm). Noon and midnight are used rather than 12 pm and 12 am; whether midnight refers to the start or the end of a date will need to be specified unless this is clear from the context.
  • 24-hour clock times have no a.m., p.m., noon or midnight suffix. Discretion may be used as to whether the hour has a leading zero (08:15 or 8:15). 00:00 refers to midnight at the start of a date, 12:00 to noon, and 24:00 to midnight at the end of a date.

Dates

  • Wikipedia does not use ordinal suffixes or articles, or put a comma between month and year in partial dates.
Incorrect February 14th, 14th February, the 14th of February
Correct 14 February, February 14
Incorrect October, 1976
Correct October 1976
  • If a date range is abbreviated, use the formats 5–7 January 1979 or September 21–29, 2002, with an unspaced en-dash. If the autoformatting function is used, the opening and closing dates of the range must be given in full (see Autoformatting and linking) and be separated by a spaced en dash.
  • Rarely, a night may be expressed in terms of the two contiguous dates using a slash (the bombing raids of the night of 30/31 May 1942); this cannot be done using the autoformatting function.
  • Yearless dates (5 March, March 5) are inappropriate unless the year is obvious from the context. There is no such ambiguity with recurring events, such as "January 1 is New Year's Day".
  • ISO 8601 dates (1976-05-31) are uncommon in English prose, and are generally not used in Wikipedia. However, they may be useful in long lists and tables for conciseness and ease of comparison.

Full date formatting

In general, the following formats are acceptable:

  • International format: 14 February and 14 February 1990 (common in many countries);
  • American format: February 14 and February 14, 1990 (more common in the US).

Disputes between editors over date formats are avoided by using three simple guidelines. See also autoformatting and linking.

Consistency within articles
The same format should be used in the main text, footnotes and references of each article, except for:
  • dates within quotations and titles, where the original format is retained;
  • explicit comparisons of date formatting.
Strong national ties to a topic
Articles on topics with strong ties to a particular English-speaking nation should generally use the more common date format for that nation; articles related to Canada may use either format consistently. Articles related to other countries that commonly use one of the two acceptable guidelines above should use that format.
Retaining the existing format
If an article has evolved using predominantly one format, the whole article should conform to that variety, unless there are reasons for changing it on the basis of strong national ties to the topic.
In the early stages of writing an article, the format chosen by the first major contributor to the article should be used, unless there is reason to change it on the basis of strong national ties to the topic. Where an article that is not a stub shows no clear sign of which format is used, the first person to insert a date is equivalent to the first major contributor.

Dates of birth and death

At the start of an article on a person, his or her dates of birth and death are provided. For example: "Charles Darwin (12 February 1809 – 19 April 1882) was a British ..."

  • Locations of birth and death are given subsequently rather than being entangled with the dates.
  • When only the years are known: "Socrates (470–399 BC) was ..."
  • For a person still living: "Serena Williams (born September 26, 1981) ...", not "... (September 26, 1981–) ..."
  • When the date of birth is unknown: "Offa (died 26 July 796) ..."
  • When the date of birth is known only approximately: "Genghis Khan (c. 1162 – August 18, 1227) ..."
  • When the dates of both birth and death are known only approximately: "Dionysius Exiguus (c. 470 – c. 540) ..."
  • When the date of death is unknown, but the person is certainly now dead: "Robert Menli Lyon (born 1789, date of death unknown) ..."
  • When only the dates of the person's reign are known, and only approximately: "Rameses III (reigned c. 1180 BCE – c. 1150 BCE) ..."
  • When the person is known to have been alive (flourishing) at certain dates, [[floruit|fl.]] is used to link to floruit, in case the meaning is not familiar: "Osmund (fl. 760–72) ..."
  • When the person is known to have been alive as early as about 660, and to have died in 685: "Aethelwalh (fl. c. 660–85) ..."

In biographical infobox templates, provide age calculation with {{birth date and age}} for living people and {{death date and age}} for the deceased when the full birth or death date, respectively, is known.

Other date ranges

Dates that are given as ranges should follow the same patterns as given above for birth and death dates. Ranges that come up to the present (as of the time that the information was added to the article) should generally be given in ways that prevent their becoming counterfactually obsolete, e.g. from 1996 onward (as of October 2007), not from 1996 to the present; "the present" is a constantly moving target. In the main text of articles, the form 1996– (with no date after the en-dash) should not be used, though it is preferred in infoboxes and other crowded templates or lists, with the caveat that they may need to be examined by editors more frequently to see if they need to be updated; it is helpful to other editors to add an HTML comment immediately after such constructions, giving the as-of date, e.g.: <!--as of 10 October 2007-->. The form since 1996 should be used in favor of 1996–present in article text and infoboxes.

Longer periods

  • Months are expressed as whole words (February, not 2), except in the ISO 8601 format. Abbreviations such as Feb are used only where space is extremely limited, such as in tables and infoboxes. Do not insert of between a month and a year (April 2000, not April of 2000).
Shortcut:
WP:SEASON
  • Seasons. Because the seasons are not simply reversed in each hemisphere – and areas near the equator tend to have just wet and dry seasons – neutral wording may be preferable (in early 1990, in the second quarter of 2003, around September). Use a date or month rather than a season name, unless there is a logical connection (the autumn harvest). Seasons are normally spelled with a lower-case initial.
  • Years
  • Years are normally expressed in digits; a comma is not used in four-digit years (1988, not 1,988).
  • Avoid inserting the words the year before the digits (1995, not the year 1995), unless the meaning would otherwise be unclear.
  • Year ranges, like all ranges, are separated by an en dash (do not use a hyphen or slash (2005–08, not 2005-08 or 2005/08)). A closing CE/AD year is normally written with two digits (1881–86) unless it is in a different century from that of the opening year (1881–1986). The full closing year is acceptable, but abbreviating it to a single digit (1881–6) or three digits (1881–886) is not. A closing BCE or BC year is given in full (2590–2550 BCE). While one era signifier at the end of a date range requires an unspaced en dash (12–5 BC), a spaced en dash is required when a signifier is used after the opening and closing years (5 BC – AD 29).
  • A slash may be used to indicate regular defined yearly periods that do not coincide with calendar years (the financial year 1993/94, the 1999/2000 snooker season).
  • To indicate around/approximately/about, the abbreviations c. and ca. are preferred over circa, approximately or approx., and are spaced (c. 1291). Do not use a question mark for this function (1291?), as this may indicate to the reader an uncertainty on the part of Wikipedia editors rather than on the part of reliable historians.
  • Decades
    • Decades as such contain no apostrophe (the 1980s, not the 1980's). The two-digit form is never used in reference to the decade as a time span per se.
    • The two-digit style, to which a preceding apostrophe is typically added, is used only in reference to a social era or cultural phenomenon that roughly corresponds to and is said to define a decade, and only if it is used in a sourceable stock phrase (the Roaring '20s, the Gay '90s), or when there is a notable connection between the period and what is being discussed in the sentence (a sense of social justice informed by '60s counterculture, but grew up in 1960s Boston, moving to Dallas in 1971). Such an abbreviation should not be used if it would be redundant ('80s Reaganomics) or if it does not have a clear cultural significance and usage (the '10s).
  • Centuries and millennia
    • There was no year 0. So for dates AD (or CE) the 1st century was 1–100, the 17th century was 1601–1700, and the second millennium was 1001–2000; for dates BC (or BCE) the 1st century was 100–1; the 17th century was 1700–1601, and the second millennium was 2000–1001.
    • Do not capitalize century or millennium unless other circumstances require it.
    • Because expressions such as the 1700s are ambiguous (referring to a century or a decade), they are best avoided.
  • Eras and other very long periods
  • Either CE and BCE or AD and BC can be used—spaced, undotted (without periods) and upper-case. Choose either the BC/AD or the BCE/CE system, but not both in the same article. Style guides generally recommend writing AD before a year (AD 1066) and after a century (2nd century AD); however, writing AD after the year (1066 AD) is also common in practice. The other abbreviations always appear after (1066 CE, 3700 BCE, 3700 BC). The absence of such an abbreviation indicates the default, CE/AD. It is inappropriate for a Wikipedia editor to change from one style to another unless there is a substantive reason; the Manual of Style favors neither system over the other.
  • Uncalibrated (bce) radiocarbon dates: Some source materials will indicate whether a date is calibrated or not simply by a change in capitalization; this is often a source of confusion for the unwary reader. Do not give uncalibrated radiocarbon dates (represented by the lower-case bce unit, occasionally bc or b.c. in some sources), except in directly quoted material, and even then include a footnote, a [square-bracketed editor's note], or other indication to the reader what the calibrated date is, or at least that the date is uncalibrated. Calibrated and uncalibrated dates can diverge surprisingly widely, and the average reader does not recognize the distinction between bce and BCE / BC.
  • Abbreviations indicating long periods of time ago—such as BP (before present), as well as various annum-based units such as ka (kiloannum), Ma (megaannum) and Ga (gigaannum) are given as full words on first occurrence. Where source quotations use the abbreviations kya (thousand years ago), mya (million years ago), or bya (billion years ago) this should be explained to the reader, as in "a measured Libby radiocarbon date of 35.1 mya" (million years ago, or 35.1 Ma) had to be calibrated against then newly available stratigraphic dating references in order to estimate a Cambridge standardized date of 36.2 Ma BP cal. The kya, mya and bya symbols are deprecated in some fields such as geophysics and geology, but remain common in others, such as anthropology.
  • BP: Do not convert other notations to BP unless you are certain of what you are doing. In some contexts the unit BP is actually defined as "years before 1950-01-01", not "years before the literal present", and the conversion may introduce an error if the date being converted is not a wide approximation (18,000 BP) but a more narrow one or an actual known year. BP years are given as 18,000 BP or spelled out as 18,000 years before present (not 18,000 YBP, 18,000 before present, 18,000 years before the present, or similar.)

Calendars

See also: Old Style and New Style dates

Dates can be given in any appropriate calendar, as long as the date in either the Julian or Gregorian calendars is provided, as described below. For example, an article on the early history of Islam may give dates in both Islamic and Julian calendars. Where a calendar other than the Julian or Gregorian is used, this must be clear to readers.

  • Current events are given in the Gregorian calendar.
  • Dates before the adoption of the Gregorian calendar on 1582-10-15 are normally given in the Julian calendar. The Julian day and month should not be converted to the Gregorian calendar, but the start of the Julian year should be assumed to be 1 January (see below for more details).
  • Dates for Roman history before 45 BC are given in the Roman calendar, which was neither Julian nor Gregorian. When (rarely) the Julian equivalent is certain, it may be included.
  • The Julian or Gregorian equivalent of dates in early Egyptian and Mesopotamian history is often debatable. Follow the consensus of reliable sources, or indicate their divergence.
  • Dates of events in countries using the Gregorian calendar are given in the Gregorian calendar. This includes some of the Continent of Europe from 1582, the British Empire from 1752-09-14, and Russia from 1918-02-14 (see the Gregorian calendar article).

The dating method used in a Wikipedia article should follow that used by reliable secondary sources. If the reliable secondary sources disagree, choose the most common used by reliable secondary sources and note the usage in a footnote.

At some places and times, dates other than 1 January were used as the start of the year. The most common English-language convention is the Annunciation Style used in Britain and its colonies, in which the year started on 25 March, Annunciation Day; see the New Year article for a list of other styles. 1 January is assumed to be the opening date for years; if there is reason to use another start-date, this should be stated.

If there is a need to mention Old Style or New Style dates in an article (as in the Glorious Revolution), a footnote should be provided on the first usage, stating whether the "New Style" refers to a start of year adjustment or to the Gregorian calendar (it can mean either).

Time zones

When writing a date, first consider where the event happened and use the time zone there. For example, the date of the Attack on Pearl Harbor should be December 7, 1941 (Hawaii time/date). If it is difficult to judge where, consider what is significant. For example, if a vandal based in Japan attacked a Pentagon computer in the United States, use the time zone for the Pentagon, where the attack had its effect. If known, include the UTC date and time of the event in the article, indicating that it is UTC.

Autoformatting and linking

Shortcuts:
MOS:UNLINKYEARS
MOS:SYL
  • A combination of a day number and a month can be autoformatted by adding square brackets ([[5 November]]). If a year is also given, with a separate link, all three items are autoformatted as a single date. The square brackets instruct the MediaWiki software to format the item according to the date preferences if a setting has been chosen by registered users. The autoformatting mechanism does not work for
  • registered users that have not made a setting
  • unregistered users.

Links to date elements that do not contain both a day number and a month are not required; for example, solitary months, solitary days of the week, solitary years, decades, centuries, and month and year combinations. Such links must not be used unless the reader needs to follow the link to understand the topic; see WP:CONTEXT. Autoformatting must not be used for the following purposes:

  • piped links to date elements ([[20 June|20]], [[20 June]] [[1997 in South African sport|1997]]) (several forms of piped links break the date formatting function);
  • links to date ranges in the same calendar month e.g. December 13–17 or the night of 30/31 May – the autoformatting mechanism will damage such dates (30/May 31);
  • links to date elements on disambiguation pages;
  • links to date elements in article and section headings; and
  • links to date elements in quotations (unless the original text was wikilinked).

The following table shows how the autoformatting mechanism behaves. The preference settings that a logged-in, registered user has chosen are displayed in the second row.

What you type What logged-in registered users see (settings on first row) What others will see*
-- January 15, 2001 15 January 2001 2001 January 15 2001-01-15 No preference --
[[May 15]] May 15 15 May May 15 May 15 May 15 May 15
[[15 May]] May 15 15 May 15 May 15 May 15 May 15 May
[[May 15]], [[2005]] May 15, 2005 15 May 2005 2005 May 15 2005-05-15 May 15, 2005 May 15, 2005
[[15 May]] [[2005]] May 15, 2005 15 May 2005 2005 May 15 2005-05-15 15 May 2005 15 May 2005
[[2005-05-15]] May 15, 2005 15 May 2005 2005 May 15 2005-05-15 2005-05-15 2005-05-15
* Non-registered users and registered users not logged in
  • The year should be wikilinked separate from the date except for dates in ISO 8601 format. Other full date formats will not autoformat when wikilinked, and are likely to produce a redlink: [[2005 May 15]] produces 2005 May 15.

Numbers

Numbers as figures or words

In the body of an article, single-digit whole numbers from zero to nine are spelled out in words; numbers greater than nine may be rendered in numerals or may be rendered in words if they are expressed in one or two words (sixteen, eighty-four, two hundred, but 3.75, 544, 21 million).

Exceptions

  • Numbers in mathematical formulas are never spelled out (3 < π < 22/7, not three < π < 22 sevenths).
  • The numerical elements of dates and times are not normally spelled out (that is, do not use the seventh of January or twelve forty-five p.m.). Spell them out in historical references, such as Seventh of March speech and Fifth of November.
  • Numbers that begin a sentence are spelled out; alternatively, the sentence can be recast so that a figure does not begin the sentence.
  • In tables and infoboxes, all numbers are expressed as numerals when offered as data. Numbers within a table's expounding text and comments should be consistent with the general rule.
  • Within a context or a list, style should be consistent (either 5 cats and 32 dogs or five cats and thirty-two dogs, not five cats and 32 dogs).
  • Where numerals may cause confusion, use words instead (thirty-six 6.4-inch rifled guns, not 36 6.4-inch rifled guns).
  • Fractions are normally spelled out; use the fraction form if they occur in a percentage or with an abbreviated unit (⅛ mm or an eighth of a millimeter, but never an eighth of a mm) or if they are mixed with whole numerals.
  • Decimal representations containing a decimal point are not spelled out (1.00, 3.14159).
  • Where a whole number in a percentage is spelled out, the percent sign is not used (three percent or 3%, not three %).
  • Ordinal numbers are spelled out using the same rules as for cardinal numbers. The exception is ordinals for centuries, which are expressed in digits (the 5th century CE; 19th century painting). The ordinal suffix (e.g., th) is not superscripted (23rd and 496th, not 23rd and 496th). Spell out ordinal numbers when they are inclusive used as the first word of a proper name (e.g. Fourth Amendment; Seventeenth Judicial District). Do not spell out ordinal numbers in the proper names of military units.
  • Proper names and formal numerical designations comply with common usage (Chanel No. 5, 4 Main Street, 1-Naphthylamine, Channel 6). This is the case even where it causes a numeral to open a sentence, although this is usually avoided by rewording.
  • The numeral and the spelled-out number can have different meanings, as in these two phrases:
    • Every number except one, in which one refers to the number of exceptions (for example, the one exception could be the number 42), although rephrasing to avoid the ambiguity would be better; and
    • Every number except 1, in which the specific number 1 is the exception (this usage is not ambiguous).

Hyphenation

  • Spelled-out two-word numbers from 21 to 99 are hyphenated (fifty-six), as are fractions (seven-eighths). Do not hyphenate other multi-word numbers (five hundred, not five-hundred).

Large numbers

See also: Order of magnitude and Long and short scales
  • Commas are used to break the sequence every three places left of the decimal point; spaces or dots are never used in this role (2,900,000, not 2 900 000).
  • Large rounded numbers are generally assumed to be approximations; only where the approximation could be misleading is it necessary to qualify with about or a similar term.
  • Avoid overly precise values where they are unlikely to be stable or accurate, or where the precision is unnecessary in the context (The speed of light in a vacuum is 299,792,458 metres per second is probably appropriate, but The distance from the Earth to the Sun is 149,014,769 kilometres and The population of Cape Town is 2,968,790 would usually not be, because both values are unstable at that level of precision, and readers are unlikely to care in the context.)
  • Scientific notation (5.8 × 107) is preferred in scientific contexts.
  • Where values in the millions occur a number of times through an article, upper-case M may be used for million, unspaced, after spelling out the first occurrence. (She bequeathed her fortune of £100 million unequally: her eldest daughter received £70M, her husband £18M, and her three sons £4M each.)
  • Billion is understood as 109 (short scale). After the first occurrence in an article, billion may be abbreviated to unspaced bn ($35bn). Where the alternative meaning 1012 (long scale) is required for some reason, a footnote or inline comment is appropriate. Except in computing and certain scientific contexts, giga- or its symbol G is inappropriate.

Decimal points

  • A decimal point is used between the integer and the fractional parts of a decimal; a comma is never used in this role (6.57, not 6,57).
  • The number of decimal places should be consistent within a list or context (The response rates were 41.0 and 47.4 percent, respectively, not The response rates were 41 and 47.4 percent, respectively).
  • Numbers between negative one and positive one require a leading zero (0.02, not .02); exceptions are sporting performance averages (.430 batting average) and commonly used terms such as .22 caliber.

Percentages

  • Percent or per cent are commonly used to indicate percentages in the body of an article. The symbol % is more common in scientific or technical articles and in complex listings.
  • The symbol is unspaced (71%, not 71 %).
  • In tables and infoboxes, the symbol % is normally preferred to the spelled-out percent or per cent.
  • Ranges are preferably formatted with one rather than two percentage signifiers (22–28%, not 22%–28%).
  • Avoid ambiguity in expressing a change of rates. This can be done by using percentage points, not percentages, to express a change in a percentage or the difference between two percentages; for example, "The agent raised the commission by five percentage points, from 10 to 15%" (if the 10% commission had instead been raised by 5%, the new rate would have been 10.5%). It is often possible to recast the sentence to avoid the ambiguity ("made the commission larger by half."). Percentage point should not be confused with basis point, which is a hundredth of a percentage point.

Natural numbers

The set of natural numbers has two common meanings: {0,1,2,3,…}, which may also be called non-negative integers, and {1,2,3,…}, which may also be called positive integers. Use the sense appropriate to the field to which the subject of the article belongs if the field has a preferred convention. If the sense is unclear, and if it is important whether or not zero is included, consider using one of the alternative phrases rather than natural numbers if the context permits.

Repeating decimals

The preferred way to indicate a repeating decimal is to place a bar over the digits that repeat. To achieve this the template {{overline}} can be used. For example, the markup 14.{{overline|285714}} gives "14.285714".

Consider a short explanation of the notation the first time this notation is used in an article. Some authors place the repeating digits in parentheses rather than using an overbar (perhaps because overbars are not available in their typesetting environment) but this should be avoided in Wikipedia to avoid confusion with expressing uncertainty.

Non-base-10 notations

For numbers expressed in bases other than base ten:

  • In computer-related articles, use the C programming language prefixes 0x (zero-ex) for hexadecimal and 0 (zero) for octal. For binary, use 0b. Consider including a note at the top of the page about these prefixes.
  • In all other articles, use subscript notation. For example: 1379, 2416, 2A912, A87D16 (use <sub> and </sub>).
  • For base eleven and higher, use whatever symbols are conventional for that base. One quite common convention, especially for base 16, is to use upper-case A–F for digits from 10 through 15 (0x5AB3).

Scientific notation, engineering notation, and uncertainty

Notations

  • Scientific notation is done in the format of 1 leading digit/decimal marker/rest of digits/×10n, where n is the integer that gives one leading digit.
  • 1.602×10−19 is a proper use of scientific notation.
  • 160.2×10−17 is not a proper use of scientific notation.
  • Engineering notation is done in the format of leading digits/decimal marker/rest of digits/×10n, where n is a multiple of 3. The number of leading digits is adjusted accordingly.
  • 132.23×106 is a proper use of engineering notation.
  • 1.3223×108 is a not proper use of engineering notation.
  • When using either scientific or engineering notation in articles, consistency is preferred (e.g., do not write A 2.23×102 m region covered by 234×106 grains of sand.
  • Use discretion when it comes to using scientific and engineering notation. Not all values need to be written in it (e.g., do not write the house was 1.25×102 y old, but rather the house was 125 years old in 2008) or simply the house was built in 1883.
  • Sometimes it is useful to compare values with the same power of 10 (often in tables) and scientific or engineering notation might not be appropriate.

Uncertainty

  • Uncertainties can be written in various ways:
  • Value/±/uncertainty/×/10n/unit symbol (e.g. 1.534±0.35×1023 m
  • Do not group value and uncertainty in parenthesis before the multiplier (e.g. do not write (15.34±0.35) × 1023 m)
  • Value/superscript positive uncertainty/subscript negative uncertainty/×/10n/unit symbol (e.g. 15.34+0.43−0.23×1023 m)
  • Value(uncertainty in the last digits)/×/10n/unit symbol (e.g. 1.604(48)×10−4 J)
  • Value/±/relative uncertainty(percent)/unit symbol (e.g 12.34 ± 5% m2)
  • {{val}} is meant to be used to automatically handle all of this, but currently has known bugs, principal among them, not displaying some values as typed in the code (see Talk:val). Use with great consideration and always check that it will give the correct results before using it.

Units of measurements

Shortcut:
WP:UNITS

Guidance for usage of units of measurement is based on the following principles:

  • Unambiguousness: Do not write so you can be understood, write so you cannot be misunderstood.
  • Familiarity: The less one has to look up definitions, the easier it is to be understood.
  • International scope: Wikipedia is not country-specific, unless tackling region-specific topics, use international units.

If you have trouble balancing these three bullets, head to the talk pages to consult other editors and try to reach consensus. Mentioning the issue on the MOSNUM talk page and on the article's associated Wikiproject might also be a good idea, especially if the problem is not restricted to a specific article.

Which units to use

  • Since some disciplines use units not approved by the BIPM, or may format them in a way that differs from BIPM-prescribed format, when such units are normally used by a clear majority of relevant sources articles related to those disciplines should reflect this (e.g., using cc in automotive articles and not cm3). Such use of non-standard units are always linked on first use.
  • Familiar units are preferred over obscure units—do not write over the heads of the readership (e.g., a general interest topic such as black holes would best be served by having mass expressed in solar masses, but it might be appropriate to use Planck units in an article on the mathematics of black hole evaporation).
  • Uses of units should be consistent within an article. An article should only have one set of primary units (e.g., write A 10 kg (22 lb) bag of potatoes and a 5 kg (11 lb) bag of carrots, not A 10 kg (22 lb) bag of potatoes and an 11 lb (5 kg) bag of carrots).
  • There is consensus to use US customary units as default units in US-related topics and that it is permissible to have imperial units as primary units in UK-related topics.
  • The use of ambiguous units is discouraged (e.g., do not write gallon, but rather imperial gallon or US gallon). Only in the rarest of instances should ambiguous units be used, often in direct quotations to preserve accuracy to the quoted material.
  • Use scientific notation with discretion—not all quantities are best served by it (e.g., do not write John is 2.2×101 y old, but rather John is 22 years old).

Unit conversions

Shortcut:
MOS:CONVERSIONS
  • Conversions to and from metric units and US or imperial units should generally be provided. There are some exceptions:
  • Articles on scientific topics where there is consensus among the contributors not to convert the metric units, in which case the first occurrence of each unit should be linked.
  • When inserting a conversion would make a common expression awkward (the four-minute mile).
  • In topics such as the history of maritime law in which imperial units (e.g. miles and nautical miles) are part of the subject, it can be excessive to provide SI conversions at each instance a unit occurs. In such cases, it is best to explicitly mention that this topic will use these units without providing conversion at each instance in the lead or in the introduction, in which case the first occurrence of each unit should be linked.
  • Converted values should use a level of precision similar to that of the source value (e.g. write the Moon is approximately 380,000 kilometres (240,000 mi) from Earth, not the moon is approximately 380,000 kilometres (236,121 mi) from Earth).
  • In the main text, spell out the main units and use unit symbols or abbreviations for conversions in parentheses (e.g a pipe 5 centimetres (2 in) in diameter and 37 kilometres (23 mi) long).
  • When there is consensus to do so, the main units may also be abbreviated in the main text after the first occurrence.
  • In a direct quotation, always keep the source units.
  • Conversions required for units cited within direct quotations should appear within square brackets in the quote.
  • Alternatively, you can annotate an obscure use of units (e.g. five million board feet of lumber) with a footnote that provides conversion in standard modern units, rather than changing the text of the quotation. See the style guide for citation, footnoting and citing sources.

Unit symbols

Conventions

  • Values and unit symbols are separated by a non-breakable space (&nbsp;) (e.g., write 10 m or 29 kg, not 10m or 29kg).
  • Exceptions: Non-alphabetic symbols for degrees, minutes and seconds for angles and coordinates are unspaced (e.g., write 5° 24′ 21.12″ N for coordinates, 90° for an angle, but 18 °C for a temperature). See also Manual of Style—Geographical Coordinates.
  • Unit symbols are written in upright roman type, never in italics as they could be mistaken for dimensions, constants, or variables (e.g., write "10 m" or "29 kg", not "10 m" or "29 kg).
  • Standard symbols for units are undotted (e.g., write m for metre (not m.), kg for kilogram (not kg.), in for inch (not in., " (double quote), or ′′ (double prime)), and ft for foot (not ft., ' (single quote), or ′ (prime))).
  • Non-standard abbreviations should be dotted.
  • Symbols have no plural form—an s is never appended (e.g., write kg, km, in, lb, not kgs, kms, ins, lbs. Write bit, not bits unless bits used as a word rather than a symbol).
  • Units named after a person are not proper nouns, and thus are not capitalized when written in full (e.g., write A pascal is a unit of pressure, not A Pascal is a unit of pressure).
  • When unit names are combined by multiplication, separate them with a hyphen. A kilogram-calorie (kg·cal) is not the same thing as a kilogram calorie (kcal). Pluralization is achieved by adding an s at the end (e.g., write A force of ten newton-metres).
  • When units names are combined by division, separate them with per (e.g., write meter per second, not meter/second). Pluralization is achieved by adding an s to the unit preceding the per since it reads this many units of this per one unit of this (e.g., write An energy flow of over ten joules per second).
  • When units are combined by multiplication, use a middle dot (&middot;) to separate the symbols. For example ms is the symbol for a millisecond, while m·s is a metre-second.
  • When units are combined by division, use a slash to separate the symbols (e.g., for metre per second use the symbols m/s (not mps)) or use negative exponents (m·s−1).
  • There should be no more than one slash per compound unit symbol, e.g., kg/(m·s), not kg/m/s or kg/m·s.
  • Powers of unit symbols are expressed with a superscript exponent (write 5 km2, not 5 km^2).
  • A superscript exponent indicates that the unit is raised to a power, not the unit and the quantity (3 metres squared is 9 square metres, or 9 m2).
  • For areas and volumes, squared and cubed US customary or imperial length units may instead be rendered with sq and cu between the number and the unit symbol (write 15 sq mi and 3 cu ft, not 15 mi sq and 3 ft cu).
  • The symbols sq and cu are not used with BIPM-approved metric/SI unit symbols.
  • Numerical range of values are formatted as (lower value/en dash/higher value/non breaking space/unit symbol) (e.g., write 5.9–6.3 kg, not 5.9 kg – 6.3 kg or 5.9 – 6.3 kg), or can be specified in written form using either unit symbol or unit names, and units can be mention either after both numerical values or after the last (e.g., write from 5.9 to 6.3 kilograms, from 5.9 kilograms to 6.3 kilograms, from 5.9 to 6.3 kg and from 5.9 kg to 6.3 kg are all acceptable, but only one of these format should be in use in a given article).
  • When dimensions are given, values each number should be followed by a unit (e.g., write 1 m × 3 m × 6 m, not 1 × 3 × 6 m3 or 1 × 3 × 6 m).

Confusing units and symbols

  • The degree symbol is °. Using any other symbol (e.g., masculine ordinal º or ring above ˚) for this purpose is incorrect.
  • The symbol for the bit is bit, not b. The byte may be represented by either one of the symbols B and byte, but not b or o (French octet). Unless explicitly stated otherwise, one byte is eight bits (see Binary prefixes).
  • The symbol for Celsius degrees, Fahrenheit degrees and kelvins are °C (not C), °F (not F), and K (not °K).
  • If you need to express years as a unit, use the symbol a (from the latin annum) along with SI prefixes (e.g., write The half life of thorium-230 is 77 ka and The Cambrian is a geologic period that dates from 540 Ma to 490 Ma).
  • There are many types of years and anna (see year and annum). When years are not used in the layman's meaning (e.g., Julie is 20 years old) clarify which type of year is meant.
  • Roman prefixes are not used (M (103), MM(106), B (109)). Use SI prefixes instead.

Disambiguation

  • Identify and define ambiguous units on their first use in an article.
  • Avoid the use of unit abbreviations that have conflicting meanings in common units systems such as SI and US customary units:
  • Use nmi (or NM) to abbreviate nautical mile rather than nm (nanometre).
  • Use kn to abbreviate knot rather than kt (kilotonne).
  • Link such units to their definitions on first use.
  • Some different units share the same name. These examples show the need to be specific.
  • Use nautical mile or statute mile rather than mile in nautical and aeronautical contexts.
  • Use long ton or short ton rather than just ton (the metric unit—the tonne—is also known as the metric ton).
  • Use troy or avoirdupois ounce rather than just ounce in articles concerning precious metals, black powder, and gemstones.
  • Use fluid ounce explicitly to avoid confusion with weight, and specify, if appropriate, Imperial, U.S. or other.
  • Use US or imperial gallon rather than just gallon (and the same logic applies for quarts, pints, and fluid ounces).
  • A calorie (symbol cal) refers to a gram calorie while the kilocalorie (symbol kcal) refers to the kilogram calorie (also known as small calorie and large calorie respectively). When used in a nutrition related article, use kilogram unit as the primary unit. For articles with only a U.S. readership, use dietary calorie(s) with a one-time link to kilogram calorie.
  • In tables and infoboxes, use unit symbols and abbreviations—do not spell them out.
  • It may be appropriate to note that given quantities and conversions are approximate.
  • When part of a full sentence, write approximately in full (e.g., write Earth's radius is approximately 6,400 kilometres, not Earth's radius is approx. 6,400 kilometers or Earth's radius is ~ 6,400 kilometers).
  • In tables, infoboxes, or within brackets, use a tilde (~) or use approx. (e.g, write The capacity of a ship is sometimes expressed in gross register tons, a unit of volume defined as 100 cubic feet (~2.83 m3)).
  • Do not note a conversion as approximate where the initial quantity has already been noted as such, (e.g., write Earth's radius is approximately 6,400 km (4,000 mi), not Earth's radius is approximately 6,400  (approx. 4,000 mi).

Quantities of bytes and bits

Historical background
Prefixes for bit and byte
Decimal
Value SI
10001 k kilo-
10002 M mega-
10003 G giga-
10004 T tera-
10005 P peta-
10006 E exa-
10007 Z zetta-
10008 Y yotta-
Binary
Value IEC JEDEC
10241 Ki kibi- K kilo-
10242 Mi mebi- M mega-
10243 Gi gibi- G giga-
10244 Ti tebi-
10245 Pi pebi-
10246 Ei exbi-
10247 Zi zebi-
10248 Yi yobi-

When measuring bits and bytes, there are two different de facto standards for defining the symbols k (often written K), M, and G: one follows the International System of Units (SI) prefixes convention using powers of 1000 (103); the other uses powers of 1024 (210). The use of the prefixes K, M, G,... to represent both decimal and binary values of computer memory originates from earliest days of computing. In 1986, the Institute of Electrical and Electronics Engineers (IEEE) and the American National Standards Institute (ANSI) formally ratified such usage, making units of measure such as “kilobyte” officially mean 1024 (210) bytes, “megabyte” to mean 10242 (220) bytes, etc. However, these prefixed forms of the byte and bit were still ambiguous because the IEEE/ANSI resolution failed to reverse the practice of taking the same unit symbols (KB, MB, GB, etc.) to mean decimal values for hard-drive capacities.

In an effort to resolve this ambiguity, the International Electrotechnical Commission (IEC) introduced distinct binary prefixes in 1998. Kibi-, mebi-, gibi- (symbols Ki, Mi, Gi,...) to replace kilo-, mega-, giga. These would exclusively mean powers of 2. In 2005, the IEEE adopted the IEC proposal after a two-year trial, thus reversing its previous position. While the IEC proposal has seen a gradual adoption in the scientific literature, virtually all general-interest computer publications (both online and print), computer manufacturers, and software companies continue to follow the long-held practice in which SI-prefixed versions of byte and bit have the binary meanings for solid-state memory, and the decimal meanings for most spinning-disk mass storage. Consequently, the IEC-prefixed forms of the byte and bit, such as kibibyte and mebibyte, and their unit symbols (KiB and MiB) are unfamiliar to the typical Wikipedia reader.

Editing with byte and bit prefixes

After many years of debate, it was agreed that the prefixes K, M, G,... although familiar, were ambiguous for quantities of bits and bytes. It was also agreed that IEC prefixes, while not ambiguous, were rarely used and therefore unfamiliar. The consensus was that for the byte and bit prefixes, the spirit of the Manual of Style is better reflected by having familiar but ambiguous units, rather than unambiguous but unfamiliar units.

  • Editors should use the conventional prefixes, such as kilobyte (KB) and megabyte (MB), and disambiguate where necessary.
  • Editors should specify if the binary or decimal meanings of K, M, G,... are intended as the primary meaning. Consistency within each article is desirable, but the need for consistency may be balanced with other considerations.
  • The definition most relevant to the article should be chosen as primary one for that article (e.g., specify a binary definition in an article on RAM, and decimal definition in an article on hard drives).
  • Where consistency is not possible, specify wherever there is a deviation from the primary definition.
  • Disambiguation should be shown in bytes or bits, clearly showing the intended base (binary or decimal). There is no preference in the way to indicate the number of bytes and bits, but there should be consistency within a given article with the notation style used (e.g., write A 64 MB (64 × 10242 bytes) video card and a 100 GB (100 × 10003 bytes) hard drive, A 64 MB (64 × 220 bytes) video card and a 100 GB (100×109 bytes) hard drive or A 64 MB (67,108,864 bytes) video card and a 100 GB (100,000,000,000 bytes) hard drive are all acceptable; but not A 64 MB (67,108,864 bytes) video card and a 100 GB (100 × 10003 bytes) hard drive). Footnotes, such as those seen in Power Macintosh 5500, may be used for disambiguation.
  • The IEC prefixes are not to be used on Wikipedia except under the following circumstances:
  • when the article is on a topic where the majority of cited sources use the IEC prefixes,
  • when directly quoting a source that uses the IEC prefixes,
  • in articles specifically about or explicitly discussing the IEC prefixes.

Currencies

Shortcut:
WP:$
See also: WikiProject Numismatics: Article titles

Which one to use

  • In country-specific articles, such as Economy of Australia, use the currency of the country.
  • In non-country-specific articles such as Wealth, use US dollars (US$123), the dominant reserve currency of the world . Some editors also like to provide euro and/or UK pound sterling equivalents, formatted as described in the next section.
  • If there is no common English abbreviation or symbol, use the ISO 4217 standard.

Formatting

  • Fully identify a currency on its first appearance (AU$52); subsequent occurrences are normally given without the country identification or currency article link (just $88), unless this would be unclear. The exception to this is in articles related entirely to the US and the UK, in which the first occurrence may also be shortened and not linked ($34 and £22, respectively), unless this would be unclear. Avoid over-identifying currencies that cannot be ambiguous; e.g. do not place EU or a similar prefix before the € sign.
  • Do not place a currency symbol after the value (123$, 123£), unless the symbol is normally written thus. Likewise, do not write $US123 or $123 (US).
  • Currency abbreviations that come before the number are unspaced if they consist of or end in a symbol (£123, €123), and spaced if alphabetic (R 75).
  • Ranges are preferably formatted with one rather than two currency signifiers ($250–300, not $250–$300).
  • Conversions of less familiar currencies may be provided in terms of more familiar currencies, such as the US dollar, euro or UK pound. Conversions should be in parentheses after the original currency, rounding to the nearest whole unit, with at least the year given as a rough point of conversion rate reference; for example, 1,000 Swiss francs (US$763 in 2005).
  • For obsolete currencies, provide if possible an equivalent, formatted as a conversion, in the modern replacement currency (e.g. UK decimal pounds for historical pre-decimal pounds-and-shillings figures), or at least a US dollar equivalent as a default in cases where there is no modern equivalent.
  • When possible, always link the first occurrence of a symbol for lesser-known currencies (₮146); some editors consider it unnecessary to link the symbols of well-known currencies, but doing so can often be helpful to readers, as many countries use "dollars" or "pounds" as their base currency, and not all readers are familiar with the euro.
  • The UK pound sterling is represented by the £ symbol, with one horizontal bar. The double-barred ₤ symbol is ambiguous, as it has been used for Italian lire and other currencies as well as the British one. For non-UK currencies that use pounds or a pound symbol (e.g. the Irish punt, IR£) use the symbol conventionally preferred for that currency.

Common mathematical symbols

See also: Manual of Style (mathematics).
  • For a negative sign or subtraction operator, use a minus sign (−). You can input a minus sign by either keying in &minus; or by clicking on it in the insert box beneath the edit window (located between the ± and × signs). Do not use an en dash (–), do not use a hyphen (-) unless writing code, and do not use an em dash (—).
  • For a multiplication sign, use ×, which is input by clicking on it in the edit toolbox under the edit window or by keying in &times; (however, the letter x is accepted as a substitute for "by" in such terms as "4x4").
Common mathematical symbols
Name Operation Other use Symbol Wikicode ASCII Unicode As binary operator
(e.g. 1 + 1)		 As unary operator
(e.g. +1)
Plus sign Addition Positive sign + &plus; &#43; U+002B Spaced Unspaced
Plus or minus Addition or subtraction Positive or negative sign ± &plusmn;  ? U+00B1 Spaced Unspaced
Minus or plus Subtraction or addition Negative or positive sign ∓  ? &#x2213; U+2213 Spaced Unspaced
Minus sign Subtraction Negative sign − &minus; &#x2212; U+2212 Spaced Unspaced
Multiplication sign, cross Multiplication, vector product — × &times; &#215; U+00D7 Spaced —
Division sign, obelus Division — ÷ &divide; &#247; U+00F7 Spaced —
Equal sign Equation — =  ?  ? U+003D Spaced —
Not equal sign Non-equation — ≠  ?  ? U+2260 Spaced —
Approximate sign Approximation — ≈  ?  ? U+2248 Spaced —
Less than sign Inequation — < &lt;  ? U+2248 Spaced —
Less than or equal to Inequation — ≤  ?  ?  ? Spaced —
Greater than sign Inequation — > &gt;  ? U+2248 Spaced —
Greater than or equal to Inequation — ≥  ?  ?  ? Spaced —

Geographical coordinates

Shortcut:
WP:Coordinates

Geographical coordinates on Earth should be entered using a template to standardize the format and to provide a link to maps of the coordinates. As long as the templates are adhered to, the functions are performed automatically by a robot. Due to planned enhancements in functionality, this information is subject to change.

Two types of template are available:

  • {{coor *}}, which is used in most articles and supported by all re-users, such as Google Earth and Wikipedia-World. This however has been superseded by {{coord}} below.
  • {{coord}}, which combines the functionality of the coor family, offers users a choice of display format through user styles, emits a Geo microformat, and is supported by Google Earth.

Depending on the form of the coordinates, the following formats are available.

For just degrees, use the d mode:

{{coor d|DD|N/S|DD|E/W|}} or
{{coord|dd|N/S|dd|E/W}}

For degrees/minutes, use the dm mode:

{{coor dm|DD|MM|N/S|DD|MM|E/W|}} or
{{coord|dd|mm|N/S|dd|mm|E/W}}

For degrees/minutes/seconds, use the dms mode:

{{coor dms|DD|MM|SS|N/S|DD|MM|SS|E/W|}} or
{{coord|dd|mm|ss|N/S|dd|mm|ss|E/W}}

where:

  • latitude and longitude can be signified by decimal values in degrees
  • DD, MM, SS are the degrees, minutes, seconds, listed in sequence
  • N/S is either N or S, depending on which hemisphere, and
  • E/W is either E or W, depending on which hemisphere

For example:

for the city of Oslo, located at 59° 55′ N, 10° 44′ E, enter:

{{coor dm|59|55|N|10|44|E|}} or
{{coord|59|55|N|10|44|E}} — which becomes 59°55′N 10°44′E / 59.917, 10.733

for a country, like Botswana, less precision is appropriate:

{{coor d|22|S|24|E|}} or
{{coord|22|S|24|E}} — which becomes 22°S 24°E / -22, 24

for higher levels of precision, use the dms mode:

{{coor dms|33|56|24|N|118|24|00|W|}} or
{{coord|33|56|24|N|118|24|00|W}} — which becomes 33°56′24″N 118°24′00″W / 33.94, -118.4

London Heathrow Airport, Amsterdam, Jan Mayen and Mount Baker are examples of articles that contain geographical coordinates.

  • degrees can be specified with decimals, in d mode
  • minutes can be specified with decimals, in dm mode
  • seconds can be specified with decimals, in dms mode

Example:

{{coor d|33.94|S|118.40|W|}} or
{{coord|33.94|S|118.40|W}} or
{{coord|33.94|-118.40}}

The second and third examples become 33°56′N 118°24′W / 33.94, -118.40. The precision can be controlled by increasing or decreasing the number of decimal places. Trailing zeroes should be included.

Generally, the larger the object being mapped, the less precise the coordinates should be. For example, if just giving the location of a city, precision greater than 100 meters is not needed unless specifying a particular point in the city, for example the central administrative building. Specific buildings or other objects of similar size would justify precisions down to 10 meters or even one meter in some cases (1′′ ~15 m to 30 m, 0.0001° ~5.6 m to 10 m).

The final field, following the E/W, is available for specification of attributes, such as type, region and scale.

For more information, see the geographical coordinates WikiProject.

Templates other than {{coor *}} or {{coord}} should use the following variables for coordinates: lat_d, lat_m, lat_s, lat_NS, long_d, long_m, long_s, long_EW.

Unnecessary vagueness

Use accurate measurements whenever possible.

Vague Precise
The wallaby is small The average male wallaby is 1.6 metres (63 in) from head to tail.
Prochlorococcus marinus is a tiny cyanobacterium. The cyanobacterium Prochlorococcus marinus is 0.5 to 0.8 micrometre across.
The large oil spill stretched a long way down the Alaskan coast. The oil spill that drifted down the Alaskan coast was 3 statute miles (5 km) long and 1,000 feet (300 m) wide.

See also