Troy weight has been used to measure gold, silver and other precious metals, dating back to the Middle Ages. There are 480 grains in a troy ounce, and 12 troy ounces in 1 troy pound. In metric units, the troy ounce weighs about 31.1 grams, while a regular ounce is around 28.3 grams.
A troy ounce is slightly heavier than an ordinary ounce: there are 14.58 troy ounces in one conventional pound.
480 grain = 1 troy ounce
12 troy ounce = 1 troy pound
5,760 grain = 1 troy pound
7,000 grain = 1 avoirdupois pound
International Yard and Pound Agreement
In the International Yard and Pound Agreement of 1959, "the National Bureau of Standards and in counterpart standards group in Canada, United Kingdom, Australia, New Zealand, and South Africa" defined the value of the international grain as 0.00006479891 kilogram, so the exact value of a troy ounce is 31.10348 gram.