A troy ounce (t/oz) is an imperial weight that has been in use as a measurement of mass for Gold and Silver (and more latterly Platinum and Palladium) since the reign of Queen Elizabeth I, with the troy system of measurements dating back to the middle ages.

1 t/oz is 31.1034768 grams, with an imperial ‘avoirdupois’ ounce weighing 28.3495g.