Troy weight is a system of units of mass customarily used for precious metals and gemstones.

History

Troy weight originates from what was called the troy system of mass. Dating back to before the time of William the Conqueror, the name comes from the city of Troyes in France, an important trading city in the Middle Ages.

Units

Troy Ounce

A troy ounce, the only currently used unit of the system, is 480 grains, somewhat heavier than an avoirdupois ounce (437.5 grains). A grain is exactly 64.798 91 mg, hence one troy ounce is exactly 31.103 476 8 g, about 10 per cent more than the avoirdupois ounce, which is exactly 28.349 523 125 g. The troy ounce is the only ounce used in the pricing of precious metals, such as gold and silver, and this is the only remaining use of the troy ounce. In troy weight, there are 12 ounces in a pound, rather than 16 in the more-common avoirdupois system.

Troy Pound

A troy pound is 5760 grains (about 373.24 g), rather than 7000 (about 453.59 g).

Conversions

See also

• Carat
• Conversion of units