One troy ounce is 31.1034768 grams, or 0.0311034768 kilograms.
The troy ounce is used in the weighing and pricing of the precious metals : gold, platinum, and silver.
A troy ounce is equivalent to 480 grains. A grain is 0.06479891 grams.
A troy ounce is not the same as an imperial or avoirdupois ounce.
A troy pound is similarly non-standard. It comprises 12 troy ounces - not the traditional 16.
For extra confusion 1 kg is 32.1507466 troy ounces, co-incidentally close to the g/ozt conversion factor of 31.1034768.
A source of regular confusion and error is people dividing a kg price by 31.1034768 and hoping to get the price per troy ounce. The result, though attractively close to the right answer, is always wrong. In fact they should multiply the per kilogram price by the kg per troy ounce figure (0.0311034768) to effect the correct conversion from a per kilogram price to a per troy ounce price.
By the same reasoning a per troy ounce price of gold should be divided by kg per troy ounce figure (0.0311034768) to effect the correct conversion to a per kilogram price.
Originally coming from the French town of Troyes the troy system was the basis for the medieval British system of coinage introduced by Henry II of England.
At this time much of English administration was based on French systems. The penny was literally one pennyweight of silver. One pound sterling was equal to twenty shillings, with each shilling equal to twelve pennies. Thus, one pound sterling equals 240 pennyweights, or one troy pound of sterling silver.
The Troy system was adopted by the U.S. Mint for the regulation of coinage in 1828.