troy ounce

The troy ounce (oz t) is a unit of imperial measure, now commonly used to measure the mass (weight, in common parlance) of precious metals. One troy ounce is defined as exactly 31.1034768 g, which may be used to denote the value of a precious metal. One troy ounce of gold is denoted with the ISO 4217 currency code XAU, while one troy ounce of silver is denoted as XAG.