Troy Ounce (oz t)

The troy ounce is the unit used to weigh gold, silver, platinum and other precious metals. When a bullion coin or bar is marked "1 oz," it means one troy ounce of metal, not the ounce used for food.

It is a little heavier than the everyday ounce. In US usage, an ounce with no label is understood to be avoirdupois, so the troy unit is written with the word troy or a letter t, as in oz t (NIST Handbook 44, Appendix C).

Britain abolished the troy pound in 1879 but kept the troy ounce (NIST Handbook 44, Appendix B), and UK law allows it for trade only in gold, silver and other precious metals (Weights and Measures Act 1985, section 8).

The old riddle has a real answer. Precious metals were traditionally weighed by the troy pound of 12 troy ounces, which is 373 g, while feathers go by the everyday pound of 454 g. So the pound of feathers is heavier.

Switch to ounces and the result flips. A troy ounce of gold is 31.1 g, but an ordinary ounce of feathers is only 28.35 g.

Bullion is sold in both systems, so small bars are often sized in grams. A 10 g bar, for example, is about a third of a troy ounce (0.322 oz t).

Precious metal prices are usually quoted per troy ounce, so a price per gram is smaller by a factor of 31.1. This site does not track metal prices, but the grams to troy ounces converter turns any weight into troy ounces.