Why gold is quoted per troy ounce
Gold has been quoted per troy ounce since the era of the London gold market, and the convention stuck: COMEX futures, the LBMA benchmark, and spot FX-style XAU/USD quotes are all per troy ounce. A troy ounce weighs 31.1034768 grams — about 10% heavier than the common (avoirdupois) ounce of 28.35 grams used for everyday goods. When you see a headline gold price, it is almost always USD per troy ounce.