troy weight

UK: /trɔɪ/

WordReference Random House Unabridged Dictionary of American English © 2025

troy′ weight′, 

1. Weights and Measures 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.

• late Middle English 1425–75

Collins Concise English Dictionary © HarperCollins Publishers::

troy weight, troy / trɔɪ/ 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

Etymology: 14th Century: named after Troyes, where it was first used