The unit traditionally used to measure the weight of precious metals is the troy ounce.
An international troy ounce equals exactly 31.1034768 grams, or 480 grains. It remains the standard mass unit for much of the global bullion trade, including gold, silver, platinum, palladium, and rhodium.
The troy ounce is not the same as the ordinary avoirdupois ounce used for most household and commercial goods. An avoirdupois ounce weighs 28.349523125 grams, so a troy ounce is about 9.7% heavier. This difference matters when comparing bullion prices, coin specifications, or jewelry listings.
The troy system includes grains, pennyweights, ounces, and pounds. Twenty pennyweights make one troy ounce, while twelve troy ounces make a troy pound. The system’s name is commonly linked to Troyes, a French market town where medieval English merchants traded, though its exact origin is debated.