Pound (mass)

The pound or pound-mass (abbreviations: lb, lb_m, lbm, ℔^[1]) is a unit of mass used in the imperial, United States customary and other systems of measurement. A number of different definitions have been used, the most common today being the international avoirdupois pound which is legally defined as exactly 6999453592370000000♠0.45359237 kilograms, and which is divided into 16 avoirdupois ounces.^[2]

The unit is descended from the Roman libra (hence the abbreviation "lb"); the name pound is a Germanic adaptation of the Latin phrase libra pondo, "a pound by weight".^[3]

Usage of the unqualified term pound reflects the historical conflation of mass and weight. This accounts for the modern distinguishing terms pound-mass and pound-force.

Current use

The United States and countries of the Commonwealth of Nations agreed upon common definitions for the pound and the yard. Since 1 July 1959, the international avoirdupois pound has been defined as exactly 6999453592370000000♠0.45359237 kg.^[4][5]

In the United Kingdom, the use of the international pound was implemented in the Weights and Measures Act 1963.^[6]

The yard or the metre shall be the unit of measurement of length and the pound or the kilogram shall be the unit of measurement of mass by reference to which any measurement involving a measurement of length or mass shall be made in the United Kingdom; and- (a) the yard shall be 0.9144 metre exactly; (b) the pound shall be 0.45359237 kilogram exactly.

—Weights and Measures Act, 1963, Section 1(1)

An avoirdupois pound is equal to 16 avoirdupois ounces and to exactly 7,000 grains. The conversion factor between the kilogram and the international pound was therefore chosen to be divisible by 7, and an (international) grain is thus equal to exactly 7001647989100000000♠64.79891 milligrams. Since 1995 in Britain, the pound for weight has become obsolete, the kilo having replaced it.

Historic use

Historically, in different parts of the world, at different points in time, and for different applications, the pound (or its translation) has referred to broadly similar but not identical standards of mass or force.^[7]

Roman libra

The libra (Latin for "scales / balance") is an ancient Roman unit of mass that was equivalent to approximately 328.9 grams.^[8][9][10] It was divided into 12 uncia, or ounces. The libra is the origin of the abbreviation for pound, lb. The commonly used abbreviation lbs to indicate the plural unit of measurement does not reflect Latin usage, in which lb is both the singular and plural abbreviation.

In Britain

A number of different definitions of the pound have been used in Britain. Amongst these are the avoirdupois pound and the obsolete tower, merchant's and London pounds.^[11] The weight of precious metals when given in pounds and ounces usually assumes Troy pounds and ounces; these units are not otherwise used today.

Historically the pound sterling was a tower pound of silver. In 1528 the standard was changed to the Troy pound.

English pounds

Unit	Pounds											Ounces						Grains		Metric
	Avdp.		Troy		Tower		Merchant		London		Metric	Avdp.		Troy		Tower		Troy	Tower	g	kg
Avoirdupois	1		175/144	= 1.21527	35/27	= 1.296	28/27	= 1.037	35/36	= 0.972	≈ 0.9072	16		14 7/12	= 14.583	15 5/9	= 15.5	7000	09955 5/9	≈ 454	≈ 5/11
Troy	144/175	≈ 0.8229	1		16/15	= 1.06	64/75	= 0.853	4/5	= 0.8	≈ 0.7465	13 29/175	≈ 13.17	12		12 4/5	= 12.8	5760	08192	≈ 373	≈ 3/8
Tower	27/35	≈ 0.7714	15/16	= 0.9375	1		4/5	= 0.8	3/4	= 0.75	≈ 0.6998	12 12/35	≈ 12.34	11 1/4	= 11.25	12		5400	07680	≈ 350	≈ 7/20
Merchant	27/28	≈ 0.9643	75/64	= 1.171875	5/4	= 1.25	1		15/16	= 0.9375	≈ 0.8748	15 3/7	≈ 15.43	14 1/16	= 14.0625	15		6750	09600	≈ 437	≈ 7/16
London	36/35	≈ 1.029	5/4	= 1.25	4/3	= 1.3	16/15	= 1.06	1		≈ 0.9331	16 16/35	≈ 16.46	15		16		7200	10240	≈ 467	≈ 7/15
Metric		≈ 1.1023		≈ 1.3396		≈ 1.4290		≈ 1.1431		≈ 1.0717	1		≈ 17.64		≈ 16.08		≈ 17.15	7716	10974	= 500	= 1/2

Avoirdupois pound

The avoirdupois pound, also known as the wool pound, first came into general use c. 1300. It was initially equal to 6992 troy grains. The pound avoirdupois was divided into 16 ounces. During the reign of Queen Elizabeth, the avoirdupois pound was redefined as 7,000 troy grains. Since then, the grain has often been an integral part of the avoirdupois system. By 1758, two Elizabethan Exchequer standard weights for the avoirdupois pound existed, and when measured in troy grains they were found to be of 7,002 grains and 6,999 grains.^[12][13]

Imperial Standard Pound

In the United Kingdom, weights and measures have been defined by a long series of Acts of Parliament, the intention of which has been to regulate the sale of commodities. Materials traded in the marketplace are quantified according to accepted units and standards in order to avoid fraud. The standards themselves are legally defined so as to facilitate the resolution of disputes brought to the courts; only legally defined measures will be recognised by the courts. Quantifying devices used by traders (weights, weighing machines, containers of volumes, measures of length) are subject to official inspection, and penalties apply if they are fraudulent.

The Weights and Measures Act of 1878 marked a major overhaul of the British system of weights and measures, and the definition of the pound given there remained in force until the 1960s. The pound was defined thus (Section 4) 'The ... platinum weight ... deposited in the Standards department of the Board of Trade ... shall continue to be the imperial standard of ... weight ... and the said platinum weight shall continue to be the Imperial Standard for determining the Imperial Standard Pound for the United Kingdom'. Paragraph 13 states that the weight 'in vacuo' of this standard shall be called the Imperial Standard Pound, and that all other weights mentioned in the act and permissible for commerce shall be ascertained from it alone. The First Schedule of the Act gave more details of the standard pound:- It is a platinum cylinder nearly 1.35 inches high, and 1.15 inches diameter, and the edges are carefully rounded off. It has a groove about 0.34 inches from the top, to allow the cylinder to be lifted using an ivory fork. It was constructed following the destruction of the Houses of Parliament by fire in 1834, and is stamped P.S. 1844, 1 lb (P.S. stands for 'Parliamentary Standard'). This definition of the Imperial pound remains unchanged.

Relationship to the kilogram

The 1878 Act said that contracts worded in terms of metric units would be deemed by the courts to be made according to the Imperial units defined in the Act, and a table of metric equivalents was supplied so that the Imperial equivalents could be legally calculated. Thus defining, in UK law, metric units in terms of Imperial ones. The equivalence for the pound is given as 1 lb = 6999453592650000000♠453.59265 g or 0.45359 kg, which would make the kilogram weigh approximately 6999999999400419480♠2.2046213 lb. In 1883, it was determined jointly by the Standards Department of the Board of Trade and the Bureau International that 6999453592427700000♠0.4535924277 kg was a better approximation, and this figure, rounded to 6999453592430000000♠0.45359243 kg was given legal status by an Order in Council in May 1898.^[14]

However in 1963 a new Weights and Measures Act reversed this relationship and the pound was defined for the first time as a mass equal to 6999453592370000000♠0.45359237 kg to match the definition of the international pound agreed in 1959.

Troy pound

A troy pound is equal to 12 troy ounces and to 5,760 grains, that is exactly 7002373241721600000♠373.2417216 grams.^[15] Troy weights were used in England by apothecaries and jewellers.

Troy weight probably takes its name from the French market town of Troyes in France where English merchants traded at least as early as the early 9th century.^[16]

The troy pound is no longer in general use or legal unit for trade. In the United Kingdom, the use of the troy pound was abolished on 6 January 1879 by the WMA Weights and Measures Act of 1878, though the troy ounce was retained. The troy ounce is still used for measurements of precious metals such as gold, silver, and platinum, and sometimes gems such as opals.

Most measurements of the mass of precious metals using pounds refer to troy pounds, even though it is not always explicitly stated that this is the case. Some notable exceptions are:

• Encyclopædia Britannica which uses either avoirdupois pounds or troy ounces, likely never both in the same article, and
• the mass of Tutankhamun's sarcophagus lid. This is 110 kilograms. It is often stated to have been 242 or 243 avoirdupois pounds but sometimes, much less commonly, it is stated as 296 (troy) pounds.

Tower pound

The system called tower weight was the more general name for King Offa's pound. This dates to 757 AD and was based on the silver penny. This in turn was struck over Arabic dirhams (2d). The pound was based on the weight of 120 Arabic silver dirhams, which have been found in Offa's Dyke. The same coin weight was used throughout the Hanseatic League.

The mercantile pound (1304) of 6750 troy grains, or 9600 tower grains, derives from this pound, as 25 shilling-weights or 15 tower ounces, for general commercial use. Multiple pounds based on the same ounce were quite common. In much of Europe, the apothecaries' and commercial pounds were different numbers of the same ounce.

The tower system was referenced to a standard prototype found in the Tower of London and ran concurrently with the avoirdupois and troy systems, until the reign of Henry VIII when a royal proclamation dated 1526 required the Troy pound to be used for mint purposes instead of the Tower pound.^[17] No standards of the Tower pound are known to have survived.^[18]

The tower pound is equivalent to about 350 grams.^[19][20]

1 mercantile pound (15 oz)	=	9,600 tower grains	=	6,750 troy grains
1 tower pound (12 oz)	=	7,680 tower grains	=	5,400 troy grains
1 tower ounce (20 dwt)	=	640 tower grains	=	450 troy grains
1 tower pennyweight (dwt)	=	32 tower grains	=	22½ troy grains

Merchants' pound

The merchants' pound (mercantile pound, libra mercantoria, or commercial pound) was considered to be composed of 25 rather than 20 Tower shillings of 12 pence.^[21] It was equal to 9,600 wheat grains (15 tower ounces or 6,750 grains)^[16] and was used in England until the 14th century^[16] for goods other than money and medicine ("electuaries").^[21]

London pound

The London pound is that of the Hansa, as used in their various trading places. This is based on 16 tower ounces, each ounce divided as the tower ounce. It never became a legal standard in England; the use of this pound waxed and waned with the influence of the Hansa itself.

A London pound was equal to 7,200 troy grains (16 tower ounces or, equivalently, 15 troy ounces).

1 London pound	=	1⅓ tower pounds	=	7,200 troy grains
1 London ounce	=	1 tower ounce	=	450 troy grains
1 London pennyweight	=	1 tower pennyweight	=	22½ troy grains

In the United States

In the United States, the avoirdupois pound as a unit of mass has been officially defined in terms of the kilogram since the Mendenhall Order of 1893. That Order defined the pound to be 2.20462 pounds to a kilogram. The following year this relationship was refined as 2.20462234 pounds to a kilogram, following a determination of the British pound.^[14]

According to a 1959 NIST publication, the United States 1894 pound differed from the international pound by approximately one part in 10 million.^[2] The difference is so insignificant that it can be ignored for almost all practical purposes.^[22]

Byzantine litra

The Byzantines used a series of measurements known as pound (Latin: libra, Greek: λίτρα, litra). The most common was the logarikē litra (λογαρική λίτρα, "pound of account"), established by Constantine the Great in 309/310. It formed the basis of the Byzantine monetary system, with one litra of gold equivalent to 72 solidi. A hundred litrai were known as a kentēnarion (κεντηνάριον, "hundredweight"). Its weight seems to have decreased gradually from the original 324 grams to 319. Due to its association with gold, it was also known as the chrysaphikē litra (χρυσαφική λίτρα, "gold pound") or thalassia litra (θαλάσσια λίτρα, "maritime pound"), but it could also be used as a measure of land, equalling a fortieth of the thalassios modios.^[23]

The soualia litra was specifically used for weighing olive oil or wood, and corresponded to 4/5 of the logarikē, i.e. 256 g. Some outlying regions, especially in later times, adopted various local measures, based on Italian, Arab or Turkish measures. The most important of these was the argyrikē litra (αργυρική λίτρα, "silver pound") of 333 g, found in Trebizond and Cyprus, and probably of Arab origin.^[23]

French livre

Since the Middle Ages, various pounds (livre) have been used in France. Since the 19th century, a livre has referred to the metric pound, 500g.

The livre esterlin was equivalent to about 367.1 grams (5,665 gr) and was used between the late 9th century and the mid-14th century.^[24]

The livre poids de marc or livre de Paris was equivalent to about 489.5 grams (7,555 gr) and was used between the 1350s and the late 18th century.^[24] It was introduced by the government of John II.

The livre métrique was set equal to the kilogram by the decree of 13 Brumaire an IX between 1800 and 1812. This was a form of official metric pound.^[24]

The livre usuelle (customary unit) was defined as 500 grams, by the decree of 28 March 1812. It was abolished as a unit of mass effective 1 January 1840 by a decree of 4 July 1837,^[24] but is still used informally.

German and Austrian Pfund

Originally derived from the Roman libra, the definition varied throughout Germany in the Middle Ages and onward. The measures and weights of the Habsburg monarchy were reformed in 1761 by Empress Maria Theresia of Austria.^[25] The unusually heavy Habsburg (civil) pound of 16 ounces was later defined in terms of 560.012 grams. Bavarian reforms in 1809 and 1811 adopted essentially the same standard pound. In Prussia, a reform in 1816 defined a uniform civil pound in terms of the Prussian foot and distilled water, resulting in a Prussian pound of 467.711 grams.

Between 1803 and 1815 all German regions west of the River Rhine were French, organised in the departements: Roer, Sarre, Rhin-et-Moselle, and Mont-Tonnerre. As a result of the Congress of Vienna these became part of various German states. However, many of these regions retained the metric system and adopted a metric pound of precisely 500 grams. In 1854 the pound of 500 grams also became the official mass standard of the German Customs Union, but local pounds continued to co-exist with the Zollverein pound for some time in some German states. Nowadays, the term Pfund is still in common use and universally refers to a pound of 500 grams.

Russian funt

The Russian pound (Фунт, funt) is an obsolete Russian unit of measurement of mass. It is equal to 409.51718 grams.^[26] In 1899 the Russian pound was the basic unit of weight and all other units of weight were formed from it.

Skålpund

The Skålpund was a Scandinavian measurement that varied in weight between regions. From the 17th century onward, it was equal to 425.076 grams in Sweden but was abandoned in 1889 when Sweden switched to the metric system.

In Norway the same name was used for a weight of 498.1 grams. In Denmark it equalled 471 grams.

In the 19th century Denmark followed Germany's lead and redefined the pound as 500 grams.

Jersey pound

A Jersey pound is an obsolete unit of mass used on the island of Jersey from the 14th century to the 19th century. It was equivalent to about 7,561 grains (490 grams). It may have been derived from the French livre poids de marc.^[27]

Trone pound

The trone pound is one of a number of obsolete Scottish units of measurement. It was equivalent to between 21 and 28 avoirdupois ounces (about 600-800 grams).

Metric pounds

In many countries upon the introduction of a metric system, the pound (or its translation) became an informal term for 500 grams. In German the term is Pfund, in French livre, in Dutch pond, in Spanish and Portuguese libra, in Italian libbra, and in Danish and Swedish pund.

Though not from the same linguistic origin, the Chinese jīn (斤, also known a "catty") has a modern definition of exactly 500 grams, divided into 10 liǎng (两). Traditionally about 605 grams, the jin has been in use for more than two thousand years, serving the same purpose as "pound" for the common-use measure of weight.

Hundreds of older pounds were replaced in this way. Examples of the older pounds are one of around 459 to 460 grams in Spain, Portugal, and Latin America; one of 498.1 grams in Norway; and several different ones in what is now Germany.

Although the use of the pound as an informal term persists in these countries to a varying degree, scales and measuring devices are denominated only in grams and kilograms. A pound of product must be determined by weighing the product in grams as the use of the pound is not sanctioned for trade within the European Union.^[28]

UK and US hay and straw weights

Pound(straw) was exactly equal to 0.453592338 kg. Pound(old hay) was exactly equal to 9/14 pound(straw). Pound(new hay) was exactly equal to 3/5 pound(straw)(≡ 0.2721554028 kg).^[29]

Use in weaponry

Smoothbore cannon and carronades are designated by the weight in imperial pounds of round solid iron shot of diameter to fit the barrel. A cannon that fires a six-pound ball, for example, is called a six-pounder. Standard sizes are 6, 12, 18, 24, 32 and 42 pounds; 68-pounders also exist, and other nonstandard weapons use the same scheme. See carronade.

A similar definition, using lead balls, exists for determining the gauge of shotguns.

Notes

External links

Look up pound in Wiktionary, the free dictionary.

Conversion between units

• U.S. National Institute of Standards and Technology Special Publication 811
• National Institute of Standards and Technology Handbook 130