Pound (mass)

Pound (mass)

The pound or pound-mass (abbreviations: lb, lbm, 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 0.4535923kilograms.

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 weight'.[2]

Usage of the unqualified term pound reflects the historical conflation of mass and weight resulting from the near uniformity of gravity on Earth. This accounts for the modern distinguishing terms pound-mass and pound-force.



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.[3]

British pounds

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.[4] The weight of precious metals when given in pounds and/or 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[note 1]
Unit v · ^ English-metric ratios (in grey) are approximate.

Avoirdupois pound

The avoirdupois pound was invented by London merchants in 1303. Originally it was based on independent standards. During the reign of Henry VIII of England, the avoirdupois pound was redefined as 7,000 troy grains.[citation needed] Since then, the grain has often been considered as a part of the avoirdupois system. By 1758, two 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.[5][6]

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 must be quantified according to accepted units and standards in order to avoid fraud; the standards themselves must be 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, and the definition of the Pound given there remained in force until modern times. The Pound was defined thus (Paragraph 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 gives 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 says that contracts worded in terms of metric units will be deemed by the courts to be made according to the imperial units defined in the Act, and a table of metric equivalents is supplied whereby, in such cases, the imperial equivalents may be legally calculated. This effectively defines, for the UK courts and for commerce, the metric units in terms of imperial ones. The equivalence for the pound is given as 1 lb = 453.59265 g or 0.45359 kg, which would make the kilogram weigh approximately 2.2046213 lb. In 1883, it was determined jointly by the Standards Department of the Board of Trade and the Bureau International that 0.4535924277 kg was a better approximation, and this figure, rounded to 0.45359243 kg was given legal status by an Order in Council in May 1898.[7] The Weights and Measures Acts (WMAs) of 1939 and 1958 defined the pound by reference to the WMA of 1878, so as late as 1963 the legal definition of the pound was the same as that given in 1878 (i.e. the platinum standard of 1844).

However, in the WMA of 1963 the pound was redefined for the first time as a mass (not a weight) equal to 0.45359237 kg (to match the definition of the International pound agreed in 1959), and 'For the purposes of any measurement of weight, ... the weight of any thing may be expressed... in the same terms as its mass'. The definition of the Pound mass in terms of the imperial standard pound of 1844 was also ratified. This is its present status in the United Kingdom, the same dimension and value having been ratified in the Weights and Measures Act 1985.

United States usage

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. In 1893, the relationship was specified to be 2.20462 pounds per kilogram. In 1894, the relationship was specified to be 2.20462234 pounds per kilogram. This change followed a determination of the British pound.[7]

According to a 1959 NIST publication, the international pound differed from the United States 1894 pound by approximately one part in 10 million.[8] The difference is so insignificant that it can be ignored for almost all practical purposes.[9]

International pound

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 0.45359237 kg.[10]

In the United Kingdom, the use of the international pound was implemented in the Weights and Measures Act 1963.[11]

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 64.79891 milligrams.

Troy pound

[citation needed]

A troy pound is equal to 12 troy ounces and to 5,760 grains, that is 373.2417216 grams. 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.[12]

The troy pound is no longer in general use. In Canada, Australia, the United Kingdom, and other places the troy pound is no longer a legal unit for trade (WMA 1878). In the United Kingdom, the use of the troy pound was abolished on 6 January 1879 in accordance with the WMA 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 it fell out of use and was abolished in 1527.

The tower pound is equivalent to about 350 grams.[13][14]

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 equal to 9,600 wheat grains (15 tower ounces or 6,750 grains). It was used in England until the 14th century for most goods (other than money, spices and electuaries).[12]

London pound

The London pound is that of the Hansa, as used in their various trading places. This is based on 16 of 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

Wool pound

The wool pound was equal to 6,992 grains. It was a unit of mass used to measure the weight of wool.[15][citation needed]

Roman libra

Various historic pounds from a German textbook dated 1848

The libra (Latin for "scales / balance") is an ancient Roman unit of mass that was equivalent to approximately 327 grams. 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.

Byzantine litra

The Byzantine litra, more specifically the logarikē or chrysaphikē type used for gold, was equivalent to between 319 and 324 grams. Kazhdan 1991, p. 1238

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.[16]

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.[16] 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.[16]

The livre usuelle 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,[16] 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.[17] The unusually heavy Habsburg (civil) pound of 16 ounces was later (after the kilogram was defined) found to be 560.012 g. 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 g.

Between 1803 and 1815 all German regions west of the River Rhine were French, organised in the départements 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 the French système usuel with the metric pound of precisely 500 g. In 1854 the pound of 500 g also became the official mass standard of the German Customs Union, but states differed in the way they subdivided it (decimally, in 30 parts or in 32 parts), and 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 g.

Russian funt

The Russian pound (Фунт, funt) is an obsolete Russian unit of measurement of mass. It is equal to 409.51718 grams.[18]


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. It 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, and in Denmark it equalled 471 grams.

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

20 skålpund = 1 lispund

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.[19]

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,

The Dutch pond is an exception. It was officially redefined as 1 kilogram, with an ounce of 100 grams, but people seldom use it this way. In daily life pond is exclusively used for amounts of 500 grams, and to a lesser extent, ons for 100 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 jin (also known a "catty") has a modern definition of exactly 500 grams, divided into ten cun. 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.[20]

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.


  1. ^ "unicode chart 2100-214F". character 2114 of the Unicode 6.0 and 5.0 standards. Unicode Consortium. http://unicode.org/charts/PDF/U2100.pdf. Retrieved 28 April 2011. 
  2. ^ Oxford English Dictionary, s.v. 'pound'
  3. ^ The pound is often described as a unit of "weight", and the word "weight" can refer to either mass or force depending on context. Historically and in common parlance, "weight" refers to mass, but weight as used in modern physics is a force.
  4. ^ Grains and drams, ounces and pounds, stones and tons. Personal notes.
  5. ^ Skinner, F.G. (1952). "The English Yard and Pound Weight". Bulletin of the British Society for the History of Science 1 (7): 179. doi:10.1017/S0950563600000646. 
  6. ^ Henry William Chisholm. "On the science of weighing and measuring and standards of measure and weight". http://www.ebooksread.com/authors-eng/henry-william-chisholm/on-the-science-of-weighing-and-measuring-and-standards-of-measure-and-weight-hci/page-5-on-the-science-of-weighing-and-measuring-and-standards-of-measure-and-weight-hci.shtml. 
  7. ^ a b Barbrow, L.E.; Judson, L.V. (1976). Weights and measures standards of the United States – A brief history. http://physics.nist.gov/Pubs/SP447/contents.html. 
  8. ^ United States National Bureau of Standards (1959-06-25). "Notices "Refinement of values for the yard and the pound"". http://www.ngs.noaa.gov/PUBS_LIB/FedRegister/FRdoc59-5442.pdf. Retrieved 2006-08-12. 
  9. ^ United States National Bureau of Standards. "Appendix C of NIST Handbook 44, Specifications, Tolerances, and Other Technical Requirements for Weighing and Measuring Devices, General Tables of Units of Measurement". http://ts.nist.gov/WeightsAndMeasures/Publications/upload/h4402_appenc.pdf.  "In Great Britain, the yard, the avoirdupois pound, the troy pound, and the apothecaries pound are identical with the units of the same names used in the United States." (The introduction to this appendix makes it clear that the appendix is only for convenience and has no normative value: "In most of the other tables, only a limited number of decimal places are given, therefore making the tables better adopted to the average user.")
  10. ^ National Bureau of Standards, Appendix 8; National Physical Laboratory, P H Bigg et al. : Re-determination of the values of the imperial standard pound and of its parliamentary copies in terms of the international kilogramme during the years 1960 and 1961; Sizes.com: pound avoirdupois.
  11. ^ Quoted by Laws LJ in "[2002] EWHC 195 (Admin)". http://www.bailii.org/ew/cases/EWHC/Admin/2002/195.html. Retrieved 2006-08-12. 
  12. ^ a b Zupko, Ronald Edward (1985-12-01). Dictionary of Weights and Measures for the British Isles: The Middle Ages to the 20th Century. DIANE Publishing. ISBN 087169168X. 
  13. ^ "Weights used for gold". Tax Free Gold. http://www.taxfreegold.co.uk/weights.html. Retrieved 2011-01-14. 
  14. ^ "A brief history of the pound". The Dozenal Society of Great Britain. http://www.dozenalsociety.org.uk/history/poundhist.html. Retrieved 2011-01-14. 
  15. ^ "English Weights & Measures (personal notes)". http://home.clara.net/brianp/weights.html. Retrieved 2006-08-12. 
  16. ^ a b c d Sizes, Inc. (2001-03-16). "Pre-metric French units of mass livre and smaller". http://www.sizes.com/units/charts/UTBLFrancemass.htm. Retrieved 2006-08-12. 
  17. ^ Hille, K.C. (1831). "Medicinal-Gewicht". Magazin für Pharmacie und die dahin einschlagenden Wissenschaften (Heidelberg): p. 268. http://books.google.com/?id=BfI3AAAAMAAJ&pg=RA2-PA268. 
  18. ^ Cardarelli, F. (2004). Encyclopaedia of Scientific Units, Weights and Measures: Their SI Equivalences and Origins (2nd ed.). Springer. p. 122. ISBN 1-8523-3682-X. http://books.google.com/?id=6KCx8Ww75VkC. 
  19. ^ Sizes, Inc. (2003-07-28). "Jersey pound". http://www.sizes.com/units/pound_jersey.htm. Retrieved 2006-08-12. 
  20. ^ The Council of the European Communities (2009-05-27). "Council Directive 80/181/EEC of 20 December 1979 on the approximation of the laws of the Member States relating to Unit of measurement and on the repeal of Directive 71/354/EEC". http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=CONSLEG:1980L0181:20090527:EN:PDF. Retrieved 2009-09-14. 

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