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The grain was the legal foundation of traditional English weight systems, [5] and is the only unit that is equal throughout the troy, avoirdupois, and apothecaries' systems of mass. [6]: C-6 The unit was based on the weight of a single grain of barley which was equal to about + 4 ⁄ 3 the weight of a single grain of wheat.
The only troy weight in widespread use is the British Imperial troy ounce and its American counterpart. Both are based on a grain of 0.06479891 gram (exact, by definition), with 480 grains to a troy ounce (compared with 437 + 1 ⁄ 2 grains for an ounce avoirdupois). The British Empire abolished the 12-ounce troy pound in the 19th century.
The 56-pound weight was used as a reference standard as late as 1588. [12] [20] A statute of Henry VIII (24 Hen 8 c. 3) made avoirdupois weights mandatory. In 1588 Queen Elizabeth increased the weight of the avoirdupois pound to 7000 grains and added the troy grain to the avoirdupois weight
The apothecaries and troy pounds are divided into 12 ounces (of 480 grains) while the avoirdupois pound has 16 ounces (of 437.5 grains). The unit of volume, the gallon , has different values in the United States and in the United Kingdom – the US fluid gallon being about 0.83 imperial gallons and the US dry gallon being about 0.97 imperial ...
Troy weight, avoirdupois weight, and apothecaries' weight are all built from the same basic unit, the grain, which is the same in all three systems. However, while each system has some overlap in the names of their units of measure (all have ounces and pounds), the relationship between the grain and these other units within each system varies.
The tower pound displayed as the weight of a pound sterling of 240 early silver pennies (original pennyweight) A tower pound is equal to 12 tower ounces and to 5,400 troy grains, which equals around 350 grams. [30] The tower pound is the historical weight standard that was used for England's coinage. [31]
In the Middle Ages, an English penny's weight was literally, as well as monetarily, 1 ⁄ 20 of an ounce and 1 ⁄ 240 of a pound of sterling silver. At that time, the pound unit in use in England was the Tower pound, equal to 7,680 Tower grains (also known as wheat grains). The medieval English pennyweight was thus equal to 32 Tower grains.
See Weight for detail of mass/weight distinction and conversion. Avoirdupois is a system of mass based on a pound of 16 ounces, while Troy weight is the system of mass where 12 troy ounces equals one troy pound. The symbol g 0 is used to denote standard gravity in order to avoid confusion with the (upright) g symbol for gram.