Troy Ounce Introduction - What is a Troy Ounce?
When someone speaks of something weighing an ounce, the chances are, that they are referring to an Avoirdupois Ounce. Unless, that is, they are referring to an ounce of gold, silver, platinum, gemstones or gunpowder: In which case, the chances are, they are referring to a Troy Ounce. The two ounces are not the same!

The prices of Gold, Silver and Platinum we hear quoted in the commodities markets, are for Troy Ounces. However, not everyone knows the difference; and if you are buying precious metals - for example gold bars online, or perhaps gold and silver on eBay (maybe with a view to profiting from an item's scrap value), you really need to be sure which type of ounce you are getting - because a Troy Ounce is over 9.7% heavier than an Avoirdupois Ounce!

An Avoirdupois Ounce is exactly 28.349523125 grams - or 437.5 grains
A Troy Ounce is exactly 31.1034768 grams - or 480 grains

Curiously, there are 12 Troy Ounces in a Troy Pound - and 16 Avoirdupois Ounces in an Avoirdupois Pound. So even though a Troy Ounce is heavier than an Avoirdupois Ounce, a Troy Pound is lighter than an Avoirdupois pound! However, the use of the Troy Pound has now been completely discontinued - thankfully for the sake of simplicity!

You also still sometimes see weights of silver bullion bars denoted in grains. (Grains are also still used in the USA in weights of certain armaments - for example, gunpowder, arrows and fencing foils.)

It's all a bit confusing, isn't it?

A little. But much less so than it must have been in ancient times. In days gone by there were other obscure systems of weights - such as the Wool Pound, Tower Pound, Mercantile Pound and London Pound - all of which are different! Most of these systems have been abolished for hundreds of years - but it is interesting to note the variations through time - and the complex challenges of maintaining "standard" weights that could be used by all. more on that in the "History of the Troy Ounce" section later.