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Pound (British Imperial)

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Wikipedia.png This page uses content from the English Wikipedia. The original article was at Pound (mass)#Imperial Standard Pound. The list of authors can be seen in the page history. As with the Units of Measurement Wiki, the text of Wikipedia is available under Creative Commons License see Wikia:Licensing.

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 (weights, weighing machines, containers of volumes, measures of length) are subject to official inspection, and penalties apply if they are fraudulent.

The Weights and Measures Act of 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 (Section 4) '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'. Paragraph 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 1.35 inches high, and 1.15 inches diameter, and the edges are carefully rounded off. It has a groove about 0.34 inches 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 (P.S. stands for 'Parliamentary Standard'). This definition of the Imperial pound remains unchanged.

Relationship to the kilogramEdit

The 1878 Act 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. Thus defining, in UK law, metric units in terms of Imperial ones. The equivalence for the pound is given as 1 lb = 453.59265 g or 0.45359 kg, which would make the kilogram weigh approximately 2.2046213 lb. In 1883, it was determined jointly by the Standards Department of the Board of Trade and the Bureau International that 0.4535924277 kg was a better approximation, and this figure, rounded to 0.45359243 kg, was given legal status by an Order in Council in May 1898.[1]

However in 1963 a new Weights and Measures Act reversed this relationship and the pound was defined for the first time as a mass equal to 0.45359237 kg to match the definition of the International avoirdupois pound agreed in 1959.


  1. Barbrow, L.E.; Judson, L.V. (1976). Weights and measures standards of the United States – A brief history. 

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