Metrication in the United States

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This label, on a bottle of Head & Shoulders shampoo, showing contents as "23.7 FL OZ (700 mL)", illustrates the conflicted state of U.S. metrication in the early 21st century.

Metrication in the United States has been unsteady. In some fields, the metric system has been used in the United States since the early 1800s. The use of metric units in lieu of or in addition to United States customary units has been gradually increasing for many years, but much of the public momentum has been lost since the 1980s, except in schools, science, and manufacturing.

[edit] 19th century

In the early 1800s, the U.S. Coast and Geodetic Survey (the government's surveying and map-making agency) used meter and kilogram standards brought from France. In 1866, Congress authorized the use of the metric system and supplied each state with a set of standard metric weights and measures.

In 1875, the United States solidified its commitment to the development of the internationally recognized metric system by becoming one of the original seventeen signatory nations to the Convention du Mètre. The signing of this international agreement concluded five years of meetings in which the metric system was reformulated, refining the accuracy of its standards. The Treaty of the Meter, also known as the "Meter Convention", established the Bureau international des poids et mesures (BIPM, International Bureau of Weights and Measures) in Sèvres, France, to provide standards of measurement for worldwide use.

In 1893, under the Mendenhall Order, metric standards, developed through international cooperation under the auspices of BIPM, were adopted as the fundamental standards for length and mass in the United States. The customary measurements – the foot, pound, quart, etc. – have been defined in relation to the meter and the kilogram ever since.

The 1895 Utah Constitution, in Article X, Section 11, originally mandated that: "The Metric System shall be taught in the public schools of the State." This section was, however, later repealed.^[1]

[edit] 20th century

The Conférence Générale des Poids et Mesures (General Conference on Weights and Measures), the governing body that has overall responsibility for the metric system, and which is made up of the signatory nations to the Treaty of the Meter, approved an updated version of the metric system in 1960. This modern system is called Le Système International d'Unités or the International System of Units, abbreviated SI.

On 10 February 1964, the National Bureau of Standards (now known as the National Institute of Standards and Technology) issued the following statement:

"Henceforth it shall be the policy of the National Bureau of Standards to use the units of the International System (SI), as adopted by the 11th General Conference of Weights and Measures (October 1960), except when the use of these units would obviously impair communication or reduce the usefulness of a report."^[2]

In 1965, the United Kingdom (the primary Commonwealth nation) began a transition to the metric system to more fully mesh its business and trade practices with those of the European Economic Community. The conversion of the United Kingdom and the other Commonwealth nations, in particular Canada, to SI created a new sense of urgency regarding the use of metric units in the United States.

In 1968, Congress authorized a three-year study of systems of measurement in the U.S., with particular emphasis on the feasibility of adopting SI. The detailed U.S. Metric Study was conducted by the Department of Commerce. A 45-member advisory panel consulted with and took testimony from hundreds of consumers, business organizations, labor groups, manufacturers, and state and local officials.

ANMC logo

The final report of the study concluded that the U.S. would eventually join the rest of the world in the use of the metric system of measurement.^[3] The study found that measurement in the United States was already based on metric units in many areas, and that it was becoming more so every day. The majority of study participants believed that conversion to the metric system was in the best interests of the nation, particularly in view of the importance of foreign trade and the increasing influence of technology in the U.S.

US metrication logo

The study recommended that the United States implement a carefully planned transition to predominant use of the metric system over a ten-year period. Congress passed the Metric Conversion Act of 1975 "to coordinate and plan the increasing use of the metric system in the United States". The Act, however, did not require a ten-year conversion period. A process of voluntary conversion was initiated, and the U.S. Metric Board was established for planning, coordination, and public education. The public education component led to a lot of public awareness of the metric system, although the public response included plenty of resistance, apathy, and even ridicule (for example, the Saturday Night Live decabet sketch).^[4] In 1981, the Board reported to Congress that it lacked the clear Congressional mandate necessary to bring about national conversion. Due to this apparent ineffectiveness, and in a Reagan effort to reduce federal spending, as well as conscious efforts by Reagan administration officials to end metrication, the Metric Board was disbanded in the fall of 1982.

This measuring cup, manufactured and sold in the U. S. circa 1980 at the height of the metrication effort, features graduations in both metric and U. S. customary units, with the metric graduations in front for right handed users.

The Board's demise increased doubts about the United States' commitment to metrication. Public and private sector metric transition slowed at the same time that the very reasons for it became more pressing: the increasing competitiveness of other nations and the demands of global marketplaces.

Congress included new encouragement for U.S. industrial metrication in the Omnibus Trade and Competitiveness Act of 1988. This legislation amended the Metric Conversion Act of 1975 and designated the metric system as "the Preferred system of weights and measures for United States trade and commerce". The legislation states that the Federal Government has a responsibility to assist industry, especially small business, as it voluntarily converts to the metric system of measurement.

1980s Road Map talking about an impending change to the metric system

Federal agencies were required by this legislation, with certain exceptions, to use the metric system in their procurement, grants, and other business-related activities by the end of 1992. While not mandating metric use in the private sector, the Federal Government has sought to serve as a catalyst in the metric conversion of the country's trade, industry, and commerce. Exceptions were allowed for the highway and construction industries. The Department of Transportation was planning to require metric units by 2000, but this plan was canceled by the 1998 highway bill TEA21.^[5] Use in the U.S. military is generally high, due, in part, to the need to work with other nations' militaries.

Some members of Congress attempted to ban use of the metric system on federal highways in 1992 and 1993.^[6][7] However, these anti-metric bills were not met with much enthusiasm by the House and failed without a vote at the time. Despite this, the National Highway System Designation Act passed in 1995 and prohibited the use of Federal-aid highway funds to convert existing signs or purchase new signs with metric units.^[8]

[edit] Mars orbiter

The use of two different systems was the root cause in the loss of the Mars Climate Orbiter in 1998. NASA specified metric units in the contract. NASA and other organizations worked in metric units, but one subcontractor, Lockheed Martin, provided thruster performance data to the team in pound force seconds instead of newton seconds. The spacecraft was intended to orbit Mars at about 150 kilometers (93 mi) altitude, but the incorrect data meant that it probably descended instead to about 57 kilometers (35 mi), burning up in the Martian atmosphere.^[9]

[edit] 21st century

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[edit] Metrication efforts

The current effort toward national metrication is based on the claim that industrial and commercial productivity, mathematics and science education, and the competitiveness of U.S. products and services in world markets would be enhanced by completing the change to the international standard measurement system based on metric units. Many or most Americans, however, remain unconvinced of this position, or disagree over whether and how to pay and enforce complete conversion. They feel that, if undertaken, it could possibly incur considerable expense in the near term for millions of businesses and government agencies.

A potential problem for current metrication efforts is that many or most U.S. citizens, thirty years after the 1970s metric push, have little interest in metric usage. Daily life no longer features even dual usage of units such as Celsius for temperature, and American contact with metric units is limited; while most would know how much two liters of soda is, few would know what clothing to wear if it were 19 degrees Celsius outside. Those who travel overseas learn enough to get by, but most others do not feel generally compelled to use it.^[10]

[edit] Current usage

[edit] Daily life

While most people in the U.S. have heard of the metric system, metric usage remains low in daily life. Weather reports on television are given in Fahrenheit and other customary units. The majority of speed limit and road signs are in miles per hour and miles. The BTU remains the common measure of heating and cooling, and clothing is still measured in inches or sizes. Some of the more common SI prefixes are widely known, and are sometimes used with non-metric units. For example, computer hard drive capacity is measured in gigabytes and nuclear explosions are measured in kilotons and megatons of TNT. The letter K is widely accepted as meaning "thousand" (e.g., "She earned over 100K last year"). However, contrary to the SI system, this is often written with an uppercase K instead of a lowercase k. This usage has largely replaced the abbreviation m that was commonly used for "thousand" before the 1960s.

[edit] Consumer and retail

Numerous consumer products come in rounded metric-system sizes in the United States. The trend seems to be toward more product sizes based on metric units, due to the international nature of manufacturing, distribution, and sales. A few of these products display the metric quantity first or more prominently. Some items are produced and sold in rounded metric quantities (e.g., dental floss is often sold in 50 meter packages).

Perhaps the most common metric item sold is the 2-liter bottle of soft drinks. Some supermarket chains also make their store brand soft drinks available in 3-liter party sizes as well. Half-liter and one-liter containers of soft drinks are sometimes sold alongside more popular 12 fl oz, 16 fl oz, 20 fl oz, and 24 fl oz (355, 473, 591, and 710 mL) sizes. However, attempts to sell 3- or 4-liter bottles of milk, instead of gallons (3.785 L), have been largely unsuccessful, and such bottles are almost never seen in the US. Conversely wine is sold in standard bottles of 750 mL, following the practice of the rest of the world, and a fifth of liquor, once one fifth of a U.S. gallon or 757 mL, is now commonly 750 mL, but still sometimes referred to as a 'fifth'. It is becoming increasingly common to find bottled water in half-liter and one-liter sizes, but 16 fl oz, 20 fl oz, and 24 fl oz sizes still remain popular.

Household products such as shampoo, mouthwash, and dental floss have begun to be sold in metric sizes, and PowerBars and similar products have always been sold (but not marketed) by the gram. Consumer-size photographic film is commonly sold in a 35 mm standard, although print sizes and large format films are defined in inches. The standard method for sizing tires combines millimeters for tread width but uses inches for rim diameter^[11].

Nutritional food labels typically report serving sizes in both systems but only list metric values (g or mg) for the breakdown of individual nutrients. The use of Calories (large calorie) instead of kilojoules is a case where a deprecated unit^[12] is used instead of the appropriate SI unit.

Since 1992, the federal Fair Packaging and Labeling Act (FPLA) has required consumer goods to be labeled in both customary and metric units. There is a strong effort underway by industry to amend this law to allow manufacturers to use metric-only labeling.[1] Most states in the U.S. have already adopted laws allowing metric-only labeling. [2] According to the European Community (now the EU) Directive 80/181/EEC issued on 20 December 1979, the European Union would have only allowed dual-unit labels to appear on products effective through 31 December 2009, but problems experienced during metrication efforts in the UK forced the EU to abandon this deadline.^[13] Pending the EU deadline, an amendment to the FPLA to allow metric-only labeling would allow manufacturers, both importers and exporters, to avoid the significant costs associated with having to produce two distinct types of package labels. A significant advance in American metrication could result from some products displaying metric weights and measures only. A bill to permit metric-only labeling at the federal level was to have been introduced in 2005. Significant opposition from the Food Marketing Institute, representing U.S. grocers, has delayed the introduction of the bill, which would likely pass if put to a vote.^{[dubious – discuss]} The expressed fear of the FMI is that legislation to permit metric-only labels might also somehow mandate resizing of packaging to round metric sizes (a process already well underway), which could require expensive remodeling or replacement of existing display cases. A compromise has been suggested whereby manufacturers in both the U.S. and the EU could opt for either metric-only or dual labeling, but this idea has been viewed dimly by the EU negotiators.

[edit] Construction

The construction industry has been the slowest to adopt metric units. Dimensional lumber still comes in standard nominal inch cross-section sizes (e.g., a "2-by-4" is really 1½ by 3½ in). Lengths are given in feet. Building codes are established at the local level and the U.S. has extensive building standards that are based on customary units. Because of Canada's proximity to the U.S., issues of common units still arise. (Even in other otherwise metricated countries, units customary for that country often continue to be used; for example, traditional construction in Japan still uses Japanese units predating metrication.)

A curious example of this difficulty occurs in Tom Clancy's novel Without Remorse: In preparation for a commando raid on a secret prison camp in North Vietnam, a full-scale mockup of the camp is built in Quantico, Virginia. The union construction workers are puzzled and amused by dimensions that are odd numbers of feet and fractional inches, but a few realize that these dimensions are round numbers in metric units. After the replica is built, a few of the SEALs training for the mission recognize a standardized prison camp from "some Eastern-Bloc manual".

[edit] Aviation

Aircraft heights for air traffic control and related purposes are measured in feet in the U.S. (In fact, most the world continues to use feet for aviation altitudes, with the notable exceptions of Russia, China, and a few other countries.)

[edit] Education

Most students are taught the metric system in elementary school. Instruction primarily centers on the concepts of powers of 10, the associated prefixes, and the conversion from one prefix form to another. Units of length, volume, and mass are also typically introduced through comparison with ordinary objects. The lack of popular metric usage, however, provides little reinforcement. As a result, while students might understand some of the concepts underlying the metric system, they do not necessarily have an intuitive sense of what the units mean.

In science education, students do exclusively use metric measures in experiments and equations, allowing those interested in the sciences to become familiar with the metric system. But outside of the sciences, the fundamental concept that all metric units are derived from a few base units is rarely taught.

Some non-science textbooks in the U.S. only use the metric system, in an effort to support metrication, without giving conversions, which has caused confusion. This is especially true when older students who have already internalized the US customary units from sources within and outside of school are faced with unfamiliar metric measures.

Within higher education, the metric system is universal for classes in the sciences (see below).

[edit] Electricity and energy

There are no customary U.S. units for electric current, potential difference, charge, etc., since these concepts were developed well after the international adoption of metric in science. The metric ones (ampere, volt, coulomb, etc.) have always been used. Energy is often measured in watt-hours or BTUs rather than the SI joule. The rated power of engines, electric motors, and power plant steam turbines is frequently quoted in horsepower.

Heating, cooling, and combustion power are often measured in BTUs per hour. Fuel prices are mostly given in customary units, e.g., dollars per gallon, per barrel, per thousand cubic feet, per long ton, etc. The SI term hertz has completely replaced the older term cycles per second as a unit of frequency.

[edit] Financial services

The United States was one of the first nations to introduce decimalized currency. However, until 2001, U.S. stocks were traded in fractions of dollars (½, ¼, ⅛) based on the old Spanish pieces of eight. Some commodity market prices are quoted in customary units (e.g., barrels of oil, troy ounces of gold, 40,000 lb of frozen pork bellies, etc.). The federal government reports international production figures in metric units, for instance, wheat in metric tons, but in bushels for domestic production figures.

[edit] Firearms

The U.S. continues to use the inch for caliber on many civilian and law enforcement firearms.^[14] Except for the 9 mm, most widely recognizable calibers are in inches, such as the .45, .357, or .22. The arms industry is an international one, however, and many foreign gun manufacturers design, build, and sell firearms measured in fractions of an inch (a good example is the .357 SIG caliber). The US military, reflecting its relationship with NATO, uses metric measurements for almost all weapons calibers, even when the caliber in question originated as or was derived from a different measurement. (e.g. 7.62 mm rather than .308, or 5.56 mm instead of .223).

[edit] Manufacturing

Globalization of manufacturing has led to wide adoption of metric standards, although this is not yet universal. After a confusing period where automobiles were assembled with both customary and metric fasteners in each vehicle, cars are now universally built with metric parts, with the exception of lug nuts to attach tires. Automobile engines, once named after their displacement in cubic inches (e.g., the 426 Hemi), are currently named after their rounded measurement in liters (e.g., the 6.1 L Hemi). Technical publications by industry publishers and American automakers often give engine displacements in both in cubic inches and cubic centimeters (or liters).^[15][16] For example, the specifications for the Dodge SRT-8 6.1 L Hemi state the displacement as 370 cubic inches (6,059 cc).^[17]

The electronics and computer industries largely converted to metric standards as new technologies were introduced toward the end of the 20th century. Thus, while 5-1/4 inch floppy disks were truly in 5-1/4 inch-wide packages, the replacement "3-1/2 inch" disks were actually 90 mm wide. CD/DVD disks are 120 mm in diameter, but their size is rarely mentioned; Mini CDs are sometimes called "80 mm CDs".

[edit] Military

The U.S. military uses metric measurements extensively to ensure interoperability with allied forces, particularly NATO STANAGs, "standardization agreements". Ground forces measure distances in "klicks", slang for kilometers. Most military firearms are measured in metric units, beginning with the M-14 which was introduced in 1957,^[14] although a few legacy exceptions exist, such as .50-caliber guns. Aircraft ordnance is normally measured in pounds. Heavy weapon caliber is measured in millimeters. Military vehicles are generally built to metric standards. An exception is the U.S. Navy whose guns are measured in inches and whose undersea fleet measures distances in terms of "kiloyards" (equivalent to 914.4 m), depth as "feet", and velocity, in some cases, as "feet per second". The Navy and Air Force continue to measure distance in nautical miles and speed in knots; these units are now accepted for use with SI.^[18]

[edit] Illegal drugs and controlled substances

Illegal drugs and controlled substances are often measured in metric quantities.^[19] The federal law prohibiting them defines the penalties in metric masses.^[20]

In everyday usage within its subculture, marijuana is sold using a combination of metric and American customary units. At small scales the basic unit is the gram (or fractions thereof), but for larger orders fractions of ounces and pounds are used generally starting at 1/8 ounce, which is often defined in turn as 3.5 grams.^[21] The term "kilo" is used quite commonly by those in law enforcement to describe the amount of drugs (in kilograms) seized during a drug bust. A kilo of illegal drugs (in particular cocaine) is often referred to by the slang term "key".

[edit] Science and medicine

In science, metric usage is essentially universal, consistent with worldwide usage, although additional specialized units are often utilized for specific purposes in various disciplines (such as the light-year in astronomy). Medicine is generally metric, but where interaction with patients is required, usage is often mixed. Doctors often measure a patient's weight in pounds to compute a dosage of medicine administered in grams or milliliters. Heights are measured in inches but head circumferences in centimeters. Even in many cases for which metric units are otherwise used, U.S. practice often varies from the rest of the world. For example, U.S. diabetes patients measure their blood sugar levels in milligrams per deciliter, whereas most other countries use millimoles per liter.

In hospital settings, patient data is typically recorded using metric quantities, but all interaction with patients is done with reference to U.S. customary units (i.e., patient weights might be recorded in kilograms but discussed with patients in pounds).

Meteorologists are required to have substantial knowledge of the metric system, since most observing, analysis, synoptic weather charts, and computer forecast models are all done in metric. Because most weather forecasts are issued to the public in customary units, meteorologists must also know how to convert between the two systems.

Usage among veterinarians varies, but due to the heavy emphasis on public interaction, animal weights (e.g., for cats or dogs) are nearly always recorded and reported in pounds and ounces. Usage at veterinary teaching hospitals, by contrast, favors the SI units.

In early 2007, NASA announced that it will use metric units for all operations on the lunar surface when it returns to the Moon, projected for 2020.^[22]

[edit] Sports

U.S. citizens are frequently exposed to metric units through coverage of international sporting events, particularly the Olympic Games.

Races in the U.S. are run in metric distances (e.g., the 100 meter sprint and 5 km ("5K") races). Note, however, particularly for local events, even a "5K" race is often promoted as a "3.1 mile" event, and the course markers will be at one mile (not one kilometer) intervals.

Measured distances as used in events such as shot put, high jump, and discus throw are, however, often in feet and inches, except at the international level. The field and court sizes for most popular team sports (even soccer) were originally set in non-metric units. This is reflected in American football, in which the playing field is divided into yards, and many important statistics are measured in yards. Some sporting equipment, such as skis and poles, is sold in metric units.

Bicycles, especially at the high end, are increasingly being sold and sized in metric (for example, a frame described as "21 inch" size in the past is now often labeled as a "53 cm" frame instead).

[edit] Transportation

"Valencia Rd. Tucson. 500 m" on Interstate 19

Highway speed limits are posted in miles per hour and distances are largely announced in miles, yards, or feet, although a few dual mile/km signs can be found, mostly left over from demonstration projects that are no longer supported.^[23] One exception is Interstate 19 in Arizona, due to its direct link to Mexico, which is almost completely signed in metric, except for speed limit signs. Signage on this road is, however, being converted back to customary units as they are replaced. Another exception is the turnpike section of Delaware Highway 1, which uses a kilometer-based system, in anticipation of the mid-1990s conversion in the U.S. to the metric system (which did not happen). Distances were originally signed in kilometers, but have since been replaced with standard milemarkers. The exit signs have remained metric.

Since 2000, the Manual on Uniform Traffic Control Devices has been published in both metric and American Customary Units. Metric signs, including speed signs in kilometers per hour, are now displayed in the manual even though they are not normally used on the roads and there is no definite plan to go metric yet. For visual distinction, regulatory and advisory metric speed signs have black circles around the numbers followed by "km/h" and other regulatory metric signs have yellow plates reading "METRIC" in black on top of the main signs. Officially, this means that, although not widely used, metric road signs are allowed in the United States. The UK Metric Association considers this part of the metrication ahead of the United Kingdom where metric road signs are usually illegal.^[24]

Due to their proximity to Canada, the states of Washington, Vermont, New Hampshire, Maine, and parts of Upstate New York include distances in both miles and kilometers on many highway signs, especially in municipalities close to the border, although some older signs still have miles only. Newer signs on state highways on the island of Kaua‘i in Hawai‘i also include distances in both miles and kilometers.^[25] Milemarkers along highways on the Island of Hawai'i will indicate both units whenever the whole kilometer co-ordinates with the whole mile (ex.: 5mi/8km). At least one route (U.S. Route 31) in Alabama has both mileposts and kilometer-posts.^{[citation needed]} In Houston, Texas many speed limits have km/h signs underneath the MPH signs. These are located near both airports and in the Texas Medical Center.

The U.S. territory of Puerto Rico generally uses American-style (MUTCD) signs with metric measurement on highways, displaying kilometer posts and distances in km, yet speed limit signs are in miles per hour.

Gasoline and diesel fuel are both sold by the U.S. gallon, and fuel economy is rated in miles per gallon. However, some border towns neighboring Canada display the equivalent cost in Canadian dollars per liter due to the high rate of Canadian customers crossing the border specifically to purchase gasoline at a lower tax rate.^{[citation needed]} Domestic airline flights are assigned altitudes in feet and measure speed in knots. Nautical charts show depth in fathoms and use the nautical mile for distance. (One minute of arc of latitude at the radius of the earth at sea level was the standard for one nautical mile until ca. 1929. The nautical mile is now defined as exactly 1852 meters.) Railroads use the standard gauge of 4 feet 8-1/2 inches, as does most of Europe (where it is expressed instead as 1435 mm). U.S. Federal Motor Vehicle Safety Standard 101, which governs vehicle controls and displays, permit speedometers to display miles per hour, kilometers per hour, or both. Odometers are permitted to record miles or kilometers, but must be clearly labeled as to which unit they record. In practice, virtually all U.S.-market vehicles have mile odometers and dual labeled speedometers with mile-per-hour as the primary calibration. Some vehicles with electronic speed and distance readouts can be switched between U.S. and metric units.

[edit] Hybrid units

Some measurements are done in units derived from both customary and metric units. For example:

• Power per unit length from a nuclear reactor fuel rod: kilowatts per foot
• Heat rate from a power plant: BTUs per hour per kilowatt
• Federal automobile exhaust emission standards: grams per mile
• Caffeine in beverages: milligrams per ounce

Any measurement that combines customary units with electrical units is necessarily hybrid, since there are no traditional electrical units. An example can be found in Table 8, chapter 9 of the National Electrical Code Handbook (8th ed.) where resistance of conductors per unit length is given in ohms per thousand feet.

Other units are based on customary units but use metric prefixes. For example, distance to target for a U.S. submarine is expressed in kiloyards.

[edit] Cultural impact

The continuing usage of U.S. customary units has been a cause for speculation in fiction set in the future. Many such fiction has assumed that the United States and the human race in general will use metric units in the future; however, others have considered the continuing persistence of the English system to be more likely. Additionally, writers will sometimes use customary units simply because American readers and watchers will understand the measurements; other times, they are simply used by accident. The 1966 show Star Trek, for instance, initially used U.S. customary units despite multiple Earth national origins and a setting in the 23rd century. Later, starting with "The Changeling", metric measures were used, albeit inconsistently. Later sequels to the show, such as Star Trek: The Next Generation, used the metric system exclusively.

Both the metric system and attitudes in the U.S. toward the metric system are a target of humorous jabs in shows such as The Simpsons and Futurama.^[26]

[edit] See also

• Plan for Establishing Uniformity in the Coinage, Weights, and Measures of the United States, 1790 report including proposal for decimal system based on the foot

[edit] References

[edit] External links

• NIST: The United States and the Metric System (LC 1136)
• Gometric.us
• A Metric America: A Decision Whose Time Has Come
• Metric Conversion Act of 1975
• US Metric Association (mirror link)
• Mean Mr Metric satire about the (non)conversion to metric units. One of the highest scoring submissions to the Internet Oracle. Originally written by Jim Palfreyman in October 1991.
• Waits & Measures
• A humorous and serious anti-metric system site
• Examples of metric roadsigns in the U.S.
• Metrication.US