The troy ounce is the unit of weight traditionally used for precious metals such as platinum.
1 troy ounce = 0.0311 kilograms
32.1507 troy oz = 1 kilogram
The troy ounce (troy oz) differs from the more common ounce (oz) used in the U.K. and U.S.A., being slightly heavier, with 1 troy oz = 1.097 oz.
The troy system of weight is named after the city of Troyes in France, and was widely used in Europe during the Middle Ages. It fell into disuse when other systems began to be preferred, continuing to be used only in the highly specialised fields of precious metals, gems and medicines, up to the nineteenth century. Today it is only for the trading of precious metals and gemstones.