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The distinction between mass and weight (or force) is discussed in the article on Weight . In some circumstances, ''pound'' is used as the name of a unit of Force . That usage is discussed in the article on Pound-force , a unit of force equal to the weight of a 1-pound (approximately 0.0311 Slug ) mass in the standard gravitational field at Earth's surface, '' G ''. The actual gravitational field at Earth's surface varies, but the standard gravitational acceleration is usually taken to be 32.174 ft/s&2. INTERNATIONAL POUND See Also: Avoirdupois The international avoirdupois pound is equal to exactly 453.59237 Gram s. The definition of the international pound was agreed by the United States and countries of the Commonwealth Of Nations in 1958 . In the United Kingdom , the use of the international pound was implemented in the Weights and Measures Act 1963.Quoted by Laws LJ in 1 An Avoirdupois pound is equal to 16 avoirdupois Ounce s 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 Milligram s. CONVERSION TO OTHER UNITS OF MASS The table below sets out the relationships between the avoirdupois pound and:
Each entry is the number of units corresponding to its column required to equal one unit corresponding to its row. SYSTEMS OF UNITS When using the pound (mass) as part of the system of units, often called ''engineering units'', that measures time in seconds, distance in feet, and force in pounds-force, a correction factor is required in calculations involving both mass and force due to the fact that 1 pound-force is not the same as 1 lb•ft/sec&2. See Pound-force for more information. HISTORICAL ORIGIN See Also: English unit The pound as a name for a unit of weight has a long history. The word “pound” comes from the Latin word ''pendere'', meaning “to weigh”. The Latin word ''libra'' means “ Scales, Balances " and it also describes a Roman unit of mass similar to a pound. This is the origin of the abbreviation “lb” or “” for the pound. The plural form of “lb” is the same. Though it is frequently written with an “'''s'''” at the end (lbs), this is generally considered grammatically incorrect. In the United Kingdom there is a historical link between the pound as a unit of mass and the pound as a unit of currency (the Pound Sterling ), because the unit of currency was defined in the past in terms of a specific quantity of Silver . The avoirdupois pound was invented by London merchants in 1303 . The troy pound takes its name from the French market town of Troyes in France where English merchants traded at least as early as the time of Charlemagne (early ninth century). The system of Troy Weight s was used in England by apothecaries and jewelers. Prior to a change during the reign of Henry VIII Of England (see below), the avoirdupois pound was based on independent standards which had been measured as about 7,002 troy grains. During the reign of Henry VIII Of England , the avoirdupois pound was redefined as 7,000 troy grains. Since then, the grain has often been considered as a part of the avoirdupois system. In the United Kingdom , the avoirdupois pound was defined as a unit of mass by the Weights and Measures Act of 1878, but having a very slightly different value (in relation to the kilogram) than it does now, of approximately 0.453592338 kg. (This was a measured quantity, with the independently maintained artifact still serving as the official standard for this pound.) This old value is sometimes called the imperial pound, and this definition and terminology are obsolete unless referring to the slightly-different 1878 definition. In the United States , the (avoirdupois) pound as a unit of mass has been officially defined in terms of the Kilogram since 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. The current international pound differs from the United States 1894 pound by approximately one part in 10 million.2 USE IN COMMERCE --> In the United States of America the United States Department Of Commerce , the Technology Administration , and the National Institute Of Standards And Technology (NIST) have defined the use of mass and weight in the exchange of goods under the Uniform Laws and Regulations in the areas of legal Metrology and engine fuel quality in NIST Handbook 130. NIST Handbook 130 states:
U.S. federal law, which supersedes this handbook, also defines weight, particularly Net Weight, in terms of the avoirdupois pound or mass pound. From 21CFR101 Part 101.105 - Declaration of net quantity of contents when exempt :
See also 21CFR201 Part 201.51 - "Declaration of net quantity of contents" for general labeling and prescription labeling requirements. From paragraph "a" above, although the avoirdupois pound is a measure of mass - not weight, in commerce it is used with the term "Net Weight", because "there is a firmly established general consumer usage and trade custom of declaring the contents of a liquid by weight, or a solid..." And since by definition one pound force is equal to one pound weight, this legal requirement does not burden manufacturers or consumer with new or different weights or measures. OTHER POUNDS 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 (weight). Some of these other pounds are described below. Roman libra or pound See Also: Ancient Roman units of measurement A Roman libra or pound is an ancient 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 letters lb do not require a period and is used in a singular and plural manner. The abbreviation lbs is not required. Troy pound See Also: Troy weight A Troy pound is equal to 12 troy ounces and to 5,760 Grains . Today, the grain is common to the Avoirdupois and troy systems of units of mass, and an international troy pound is equal to 373.241721 grams. 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. In the United Kingdom, the use of the troy pound was abolished on 6 January 1879 . The troy pound 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:
French livre or pound See Also: French units of measurement Mesures usuelles The livre (translated as the pound), is a French name for various units of mass since the Middle Ages. The name continues to be used today to refer to a metric pound (see below). The livre esterlin was equivalent to about 367.1 Gram s and was used between the late 9th century and the mid-14th century.3 The livre poids de marc or '''livre de Paris''' was equivalent to about 7,555 Grain s or about 489.5 Gram s and was used between the 1350 s and the late 18th century.. It was introduced by the government of King John II Of France . The livre métrique was set equal to the Kilogram or 1,000 Gram s, by the decree of ''13 Brumaire an IX'' between 1800 and 1812. This was a form of official metric pound (see below). The livre usuelle was set equal to 500 Gram s, 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 . Russian pound The Russian pound (Фунт, funt) is an Obsolete Russian Unit Of Measurement for weight. It is equal to 409.5124 g. 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 Grain s. It may have been derived from the French livre poids de marc (see above).4 Tower pound See Also: English units
This article was also a good description of the tower pound among other old measure systems: http://home.clara.net/brianp/weights.html Libra mercatoria or mercantile, merchants' or commercial pound See Also: English units A mercantile pound or '''libra mercantoria''', also known as a '''merchants' pound''' or '''commercial pound''', is an obsolete unit of mass used in England for most goods (other than money, spices and Electuaries ) until a point during the 14th century. It was equal to 9,600 wheat grains (equivalent to 6,750 Grain s). There were 12 tower ounces in a tower pound, and a merchant pound was 15 tower ounces.5 London or mercantile pound See Also: English units A London pound was equal to 7,200 grains. A London pound was 16 tower ounces or, equivalently, 15 troy ounces. Wool pound See Also: English units A Wool pound was equal to 6,992 grains. It was a unit of mass used to measure the quantity of Wool .6 Scottish or trone pound See Also: Obsolete Scottish units of measurement The trone pound is one of a number of Obsolete Scottish Units Of Measurement . It was equivalent to between 21 to 28 avoirdupois ounces. Metric pounds See Also: kilogram In many countries upon the introduction of a Metric System , the pound (or its translation) became an informal term for half of a Kilogram or 500 Gram s, often following an official redefinition of an existing unit during the 19th century. The Dutch ''pond'' is an exception. It was officially redefined as 1 kilogram, with an ounce of 100 grams. If the pound is used in the Netherlands today it is likely to refer to 500 grams; the former definition has fallen out of use. However, the 100-gram ounce remains in limited use. In daily life ''pond'' is exclusively used for amounts of 500-grams, as is ''ons'' for 100 grams. In German the term is ''Pfund'', in French '' Livre '', in Dutch ''pond'', in Spanish , ''libra'', in Portuguese and Italian ''libbra''. 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. The use of the term ''pound'' is usually forbidden for official use in trade. REFERENCES EXTERNAL LINKS Conversion between units
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