Pound (mass)
The pound or pound-mass is a unit of mass used in both the British imperial and United States customary systems of measurement. Various definitions have been used; the most common today is the international avoirdupois pound, which is legally defined as exactly 0.45359237 kilograms, and which is divided into 16 avoirdupois ounces. The international standard symbol for the avoirdupois pound is lb; an alternative symbol is lbm, #, and ℔ or ″̶.
The word 'pound' and its cognates ultimately derive from a borrowing into Proto-Germanic of the Latin expression libra pondo ('the weight measured in libra'), in which the word pondo is the ablative singular of the Latin noun pondus ('weight').
The United States and the Commonwealth of Nations agreed upon common definitions for the pound and the yard. Since 1 July 1959, the international avoirdupois pound (symbol lb) 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— — 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 with a terminating decimal representation, and an (international) grain is thus equal to exactly 64.79891 milligrams.
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.[a] The Russian pound (фунт, funt) is an obsolete Russian unit of measurement of mass. It is equal to 409.51718 g (14.445293 oz). In 1899, the funt was the basic unit of weight, and all other units of weight were formed from it; in particular, a zolotnik was 1⁄96 of a funt, and a pood was 40 funty. The Skålpund was a Scandinavian measurement that varied in weight between regions. From the 17th century onward, it was equal to 425.076 g (14.9941 oz) 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 425.076 g (14.9941 oz). In Denmark, it equalled 471 g (16.6 oz). In the 19th century, Denmark followed Germany's lead and redefined the pound as 500 g (18 oz).
Roman libra
The libra (Latin for 'scale'/'balance') is an ancient Roman unit of mass that is now equivalent to 328.9 g (11.60 oz). It was divided into 12 unciae (singular: uncia), or ounces. The libra is the origin of the abbreviation for pound, "lb".
In Britain
A number of different definitions of the pound have historically been used in Britain. Among these are the avoirdupois pound, which is the common pound used for weights, and the obsolete tower, merchants' and London pounds. The troy pound and ounce remain in use only for the weight of precious metals, especially in their trade. The weights of traded precious metals, such as gold and silver, are normally quoted just in ounces (e.g. "500 ounces") and, when the type of ounce is not explicitly stated, the troy system is assumed. The pound sterling money system, which was introduced during the reign of King Offa of Mercia (757–96), was based originally on a Saxon pound of silver. After the Norman conquest the Saxon pound was known as the tower pound or moneyer's pound. In 1528, during the reign of Henry VIII, the coinage standard was changed by parliament from the tower pound to the troy pound.
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. In 1959, the United States National Bureau of Standards redefined the pound (avoirdupois) to be exactly equal to 0.453 592 37 kilograms, as had been declared by the International Yard and Pound Agreement of that year. According to a 1959 NIST publication, the United States 1894 pound differed from the international pound by approximately one part in 10 million. The difference is so insignificant that it can be ignored for almost all practical purposes.
Byzantine litra
The Byzantines used a series of measurements known as pounds (Latin: libra, Ancient Greek: λίτρα, romanized: 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 g (11.4 oz) to 319 g (11.3 oz). 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.
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, 500 g. The livre esterlin is equivalent to about 367.1 grams (5,665 gr) and was used between the late 9th century and the mid-14th century. The livre poids de marc or livre de Paris is equivalent to about 489.5 grams (7,554 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 (customary unit) was defined as 500 g (18 oz) 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.[citation needed]
German and Austrian Pfund
Originally derived from the Roman libra, the definition varied throughout the Holy Roman Empire in the Middle Ages and onward. For example, the measures and weights of the Habsburg monarchy were reformed in 1761 by Empress Maria Theresa of Austria. The unusually heavy Habsburg (civil) pound of 16 ounces was later defined in terms of 560.012 g (19.7538 oz). Bavarian reforms in 1809 and 1811 adopted essentially the same standard as the Austrian 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 (16.4980 oz). Between 1803 and 1815, all German regions west of the River Rhine were under French control, organised in the departements: Roer, Sarre, Rhin-et-Moselle, and Mont-Tonnerre. As a result of the Congress of Vienna, these regions again became part of various German states. However, many of these regions retained the metric system and adopted a metric pound of precisely 500 g (17.64 oz). In 1854, the pound of 500 g also became the official mass standard of the German Customs Union and was renamed the Zollpfund, but local pounds continued to co-exist with the Zollverein pound for some time in some German states. Nowadays, the term Pfund is sometimes still in use and universally refers to a pound of 500 g.
Smoothbore cannon and carronades are currently 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; 60-pounders and 68-pounders also exist, along with other nonstandard weapons using the same scheme. Before the introduction of the metric system, countries that produced their own artillery generally used their national pound for these designations. See carronade. A similar definition, using lead balls, exists for determining the gauge of shotguns and shotgun shells.
