What is a Troy Ounce of Gold? Tulsa Gold and Gems

There are 28 grams in a conventional ounce and 31 grams in a troy ounce.

The troy ounce is part of the troy weights system, many aspects of which were indirectly derived from the Roman monetary system.

The Romans used bronze bars of varying weights as currency. An aes grave weighed equal to 1 pound. One twelfth of an aes grave was called an uncia, or in English an "ounce."

Later standardization would change the ounce to 1/16 of a pound (the avoirdupois ounce), but the troy ounce, which is 1/12 of a troy pound (note that a troy pound is lighter than an avoirdupois pound), has been retained for the measure of precious metals.

At 480 grains, the troy ounce is heavier than the avoirdupois ounce, which weighs 437.5 grains. A grain is 64.79891 milligrams (mg); hence one troy ounce is 31.1034768 grams (g) (exact by definition), about 10 percent more than the avoirdupois ounce, which is 28.349523125 g (exact).[1][2]

NOTE: the ounce calculation on our Gold Calculator page reflects a Postal Scale Ounce (conventional ounce). The Postal Scale Ounce is provided as a convenience to our visitor to get an idea of how much their items weigh and to calculate the amount we would pay for those items.

Source: Tulsa Gold & Gems, INC.