Carat (mass) quarters" of 15 grains troy each. Likewise, the ounce troy was divisible into 24 "ounce carats" of 20 grains troy each; the ounce carat was divisible into four "ounce grains" of 5 grains troy each; and the ounce grain was divisible into four "ounce quarters" of grains troy each. The "solidus" was also a Roman weight unit. There is literary evidence that the weight of 72 coins of the type called "solidus" was exactly 1 Roman pound, and that the weight of 1 "solidus" was 24 "siliquae". The weight of a Roman pound is generally believed to have been 327.45
Troy weight by the international yard and pound agreement of 1959 as . Therefore, the troy ounce is , compared with the avoirdupois ounce, which is 437.5 grains or approximately 28.35 grams. The troy ounce, then, is about 10% heavier (ratio 192/175) than the avoirdupois ounce. Although troy ounces are still used to weigh gold, silver, and gemstones, troy weight is no longer used in most other applications. One troy ounce of gold is denoted with the ISO 4217 currency code XAU, while one troy ounce of silver is denoted as XAG. Troy weight probably takes its name from the French market