Stone (unit)

The stone or stone weight (abbreviation: st.) is an English and imperial unit of mass now equal to 14 pounds (6.35029318 kg).

England and other Germanic-speaking countries of northern Europe formerly used various standardized "stones" for trade, with their values ranging from about 5 to 40 local pounds (roughly 3 to 15 kg) depending on the location and objects weighed. The United Kingdom's imperial system adopted the wool stone of 14 pounds in 1835. With the advent of metrication, Europe's various "stones" were superseded by or adapted to the kilogram from the mid-19th century on. The stone continues in customary use in Britain and Ireland used for measuring body weight, but was prohibited for commercial use in the UK by the Weights and Measures Act of 1985.

The name "stone" derives from the use of stones for weights, a practice that dates back into antiquity. The Biblical law against the carrying of "diverse weights, a large and a small" is more literally translated as "you shall not carry a stone and a stone (אבן ואבן), a large and a small". There was no standardized "stone" in the ancient Jewish world, but in Roman times stone weights were crafted to multiples of the Roman pound. Such weights varied in quality: the Yale Medical Library holds 10 and 50-pound examples of polished serpentine, while a 40-pound example at the Eschborn Museum (see right) is made of sandstone.

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