Troy weight

Troy weight is a system of units of mass customarily used for precious metals and gemstones. Its name comes from the city of Troyes in France, an important trading city in the Middle Ages.

In troy weight, unlike the more common avoirdupois system, there are 12 ounces in a pound, rather than 16, and a troy pound is 5760 grains (approx. 373.24 grams), rather than 7000 (approx. 453.59 grams).

A troy ounce is 480 grains (approx. 31.10 grams), somewhat heavier than an avoirdupois ounce (437.5 grains, approx. 28.35 grams).