Troy-weight

noun
1.
a system of weights in use for precious metals and gems (formerly also for bread, grain, etc.): 24 grains = 1 pennyweight (1.555 grams); 20 pennyweights = 1 ounce (31.103 grams); 12 ounces = 1 pound (0.373 kilogram). The grain, ounce, and pound are the same as in apothecaries’ weight, the grain alone being the same as in avoirdupois weight. The troy pound is no longer a standard weight in Great Britain.
noun
1.
a system of weights used for precious metals and gemstones, based on the grain, which is identical to the avoirdupois grain. 24 grains = 1 pennyweight; 20 pennyweights = 1 (troy) ounce; 12 ounces = 1 (troy) pound
troy weight
(troi)
A system of weights and measures in which the grain is the same as in the avoirdupois system, and a pound contains 12 ounces, or 5,760 grains. Troy weight is used primarily by miners and gold dealers. Compare avoirdupois weight.