Pound (mass)

The pound or pound-mass (abbreviations: lb, lb_m, lbm, ℔ ) 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'.

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.

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

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.

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. 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	≈ 15∕14	≈ 11∕10	≈ 8∕7	≈ 4∕3	≈ 10∕7	≈ 16	≈ 171∕7	≈ 173∕5	≈ 7716	≈ 10974	500	1∕2
London	≈ 14∕15	1	36∕35	16∕15	5∕4	4∕3	15	16	1616∕35	7200	10240	≈ 467	≈ 7∕15
Avoirdupois	≈ 10∕11	35∕36	1	28∕27	175∕144	35∕27	147∕12	155∕9	16	7000	99555∕9	≈ 454	≈ 9∕20
Merchant	≈ 7∕8	15∕16	27∕28	1	75∕64	5∕4	141∕16	15	153∕7	6750	9600	≈ 437	≈ 7∕16
Troy	≈ 3∕4	4∕5	144∕175	64∕75	1	16∕15	12	124∕5	1329∕175	5760	8192	≈ 373	≈ 3∕8
Tower	≈ 7∕10	3∕4	27∕35	4∕5	15∕16	1	111∕4	12	1212∕35	5400	7680	≈ 350	≈ 7∕20

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.

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

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. 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.

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. 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.

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, 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. 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.

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.

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.

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.

External links

See also wiktionary:pound in Wiktionary, the free dictionary

Conversion between units

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