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, 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 unit is descended from the Roman libra. The English word pound comes from the Roman libra pondo, and is cognate with, among others, German Pfund, Dutch pond, and Swedish pund. These units are now designated as historical and are no longer in common usage, being replaced by the metric system.
Usage of the unqualified term pound reflects the historical conflation of mass and weight. This accounts for the modern distinguishing terms pound-mass and pound-force.
Etymology
The word 'pound' and its cognates ultimately derive from a borrowing into Proto-Germanic of the Latin expression libra pondo, in which the word pondo is the ablative singular of the Latin noun pondus.Current use
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 has been defined as exactly.In the United Kingdom, the use of the international pound was implemented in the Weights and Measures Act 1963.
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 grain is thus equal to exactly.
In the United Kingdom, the process of metrication and European units of measurement directives were expected to eliminate the use of the pound and ounce, but in 2007 the European Commission abandoned the requirement for metric-only labelling on packaged goods there, and allowed for dual metric–imperial marking to continue indefinitely.
In the United States, the Metric Conversion Act of 1975 declared the metric system to be the "preferred system of weights and measures" but did not suspend use of United States customary units, and the United States is the only industrialised country where commercial activities do not predominantly use the metric system, despite many efforts to do so, and the pound remains widely used as one of the key customary units.
Historical use
Historically, in different parts of the world, at different points in time, and for different applications, the pound has referred to broadly similar but not identical standards of mass or force.Roman
The libra is an ancient Roman unit of mass that is now equivalent to. It was divided into 12 unciae, 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 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, 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].
Avoirdupois pound
The avoirdupois pound, also known as the wool pound, first came into general use c. 1300. It was initially equal to 6,992 troy grains. The pound avoirdupois was divided into 16 ounces. During the reign of Queen Elizabeth I, the avoirdupois pound was redefined as 7,000 troy grains. Since then, the grain has often been an integral part of the avoirdupois system. By 1758, two Elizabethan Exchequer 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.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 are quantified according to accepted units and standards in order to avoid fraud. The standards themselves are 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 are subject to official inspection, and penalties apply if they are fraudulent.The Weights and Measures Act 1878 marked a major overhaul of the British system of weights and measures, and the definition of the pound given there remained in force until the 1960s. The pound was defined thus : "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". Section 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 gave more details of the standard pound: it is a platinum cylinder nearly high, and diameter, and the edges are carefully rounded off. It has a groove about 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".
Redefinition in terms of the kilogram
The British Weights and Measures Act 1878 said that contracts worded in terms of metric units would be deemed by the courts to be made according to the Imperial units defined in the Act, and a table of metric equivalents was supplied so that the Imperial equivalents could be legally calculated. This defined, in UK law, metric units in terms of Imperial ones. The equivalence for the pound was given as 1 lb = or 0.45359 kg, which made the kilogram equivalent to about.In 1883, it was determined jointly by the standards department of the British Board of Trade and the Bureau International that was a better approximation, and this figure, rounded to was given legal status by an Order in Council in May 1898.
In 1959, based on further measurements and international coordination, the International Yard and Pound Agreement defined an "international pound" as being equivalent to exactly. This meant that the existing legal definition of the UK pound differed from the international standard pound by. To remedy this, the pound was again redefined in the United Kingdom by the Weights and Measures Act 1963 to match the international pound, stating: "the pound shall be 0.453 592 37 kilogramme exactly", a definition which remains valid to the present day.
The 2019 revision of the SI means that the Avoirdupois pound is now defined precisely in terms of fundamental constants, ending the era of its definition in terms of physical prototypes; by definition, it is.
Troy pound
A troy pound is equal to 12 troy ounces and to 5,760 grains, which is exactly grams. Troy weights were used in England by jewellers. Apothecaries also used the troy pound and ounce, but added the drachms and scruples unit in the apothecaries' system of weights.Troy weight may take its name from the French market town of Troyes in France where English merchants traded at least as early as the early 9th century. The troy pound is no longer in general use or a legal unit for trade, but the troy ounce, of a troy pound, is still used for measurements of gems such as opals, and precious metals such as silver, platinum and particularly gold.
Tower pound
A tower pound is equal to 12 tower ounces and to 5,400 troy grains, which equals around 350 grams. The tower pound is the historical weight standard that was used for England's coinage. Before the Norman conquest in 1066, the tower pound was known as the Saxon pound. During the reign of King Offa of Mercia, a Saxon pound of silver was used to set the original weight of a pound sterling. From one Saxon pound of silver the king had 240 silver pennies minted. In the pound sterling monetary system, twelve pennies equaled a shilling and twenty shillings equaled a pound sterling.The tower pound was referenced to a standard prototype found in the Tower of London. The tower system ran concurrently with the avoirdupois and troy systems until the reign of Henry VIII, when a royal proclamation dated 1526 required that the troy pound be used for mint purposes instead of the tower pound. No standards of the tower pound are known to have survived.
The tower pound was also called the moneyers' pound ; the easterling pound, which may refer to traders of eastern Germany, or to traders on the shore of the eastern Baltic sea, or dealers of Asiatic goods who settled at the London Steelyard wharf; and the Rochelle pound by French writers, because it was also in use at La Rochelle. An almost identical weight was employed by the Germans for weighing gold and silver.
The mercantile pound 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.