How many grams are there in a 1-ounce gold bar?

There are approximately 28.35 grams of gold in an avoirdupois ounce and 31.10 grams of gold in a troy ounce. Troy ounces are the standard unit of measurement for precious metals.

The troy ounce is almost exclusively used to measure precious metals such as silver, gold, and platinum. The avoirdupois ounce is used to measure most other goods such as foods, dyes and livestock. The troy ounce and avoirdupois ounce each have a corresponding pound unit. There are 12 troy ounces in a troy pound, and 16 avoirdupois ounces in an avoirdupois pound. Both troy and avoirdupois units originated in France.