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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 0.45359237 kilograms.

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.

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 0.45359237 kg.[3]

In the United Kingdom, the use of the international pound was implemented in the Weights and Measures Act 1963.[4]

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.

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.[5]

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.[6] 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.

Comparison of different English pounds

English pounds
Unit Pounds Ounces Grains Metric
metric Lond. avdp. merc. troy tower troy tower avdp. troy tower g kg
Metric 1 1514 1110 87 43 107 ≈ 16 ≈ 1717 ≈ 1735 ≈ 7716 ≈ 10974 500 12
London 1415 1 3635 1615 54 43 15 16 161635 7200 10240 ≈ 467 715
Avoirdupois 1011 3536 1 2827 175144 3527 14712 1559 16 7000 995559 ≈ 454 920
Merchant 78 1516 2728 1 7564 54 14116 15 1537 6750 9600 ≈ 437 716
Troy 34 45 144175 6475 1 1615 12 1245 1329175 5760 8192 ≈ 373 38
Tower 710 34 2735 45 1516 1 1114 12 121235 5400 7680 ≈ 350 720

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.[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]

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 328.9 grams.[10][11][12] 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. Template:Harvnb

French livre[]

Template:See also

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 g and was used between the late 9th century and the mid-14th century.[13]

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.[13] 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.[13]

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,[13] 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.[14] 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.[15]


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.[16]

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.[17]

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. National Bureau of Standards, Appendix 8; National Physical Laboratory, PTemplate:NbspH 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.
  4. Quoted by Laws LJ in "[2002] EWHC 195 (Admin)". http://www.bailii.org/ew/cases/EWHC/Admin/2002/195.html. Retrieved 2006-08-12. 
  5. 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.
  6. Grains and drams, ounces and pounds, stones and tons. Personal notes.
  7. 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. Zupko, Ronald Edward (1977). British weights & measures: a history from antiquity to the seventeenth century. University of Wisconsin Press. p. 7. http://books.google.com/books?ei=lX3STvkfr8qIArO6waoN&ct=result&id=pWUgAQAAIAAJ&dq=roman+libra+328.9&q=5076#search_anchor. Retrieved 27 November 2011. 
  11. Frederick George Skinner (1967). Weights and measures: their ancient origins and their development in Great Britain up to A.D. 1855. H.M.S.O.. p. 65. http://books.google.com/books?id=bDcLAQAAIAAJ&q=roman+libra+328&dq=roman+libra+328&hl=en&ei=h3vSToCVHOemiQLC24TQCw&sa=X&oi=book_result&ct=result&resnum=9&ved=0CFQQ6AEwCA. Retrieved 27 November 2011. 
  12. Chambers's encyclopaedia. 14. Pergamon Press. 1967. p. 476. http://books.google.com/books?id=Z2fQAAAAMAAJ&q=roman+libra+328&dq=roman+libra+328&hl=en&ei=h3vSToCVHOemiQLC24TQCw&sa=X&oi=book_result&ct=result&resnum=2&ved=0CDQQ6AEwAQ. Retrieved 27 November 2011. 
  13. 13.0 13.1 13.2 13.3 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. 
  14. 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. 
  15. 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. 
  16. Sizes, Inc. (2003-07-28). "Jersey pound". http://www.sizes.com/units/pound_jersey.htm. Retrieved 2006-08-12. 
  17. 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. 

External links[]

See also wiktionary:pound in Wiktionary, the free dictionary

Conversion between units[]