Troy Ounce

The full conversion table and the history of the unit are in our troy ounce guide. This entry covers what the troy ounce means when you compare prices in Australia: fine weight, gross weight and the cost per ounce in AUD.

Gross weight and fine weight

What you pay for is the fine weight: the amount of pure metal inside. The gross weight includes any alloy. Two coins that both contain one troy ounce of gold can therefore weigh different amounts on your scales:

• The Perth Mint's 1 oz Kangaroo gold bullion coin is struck in 99.99% gold, so gross and fine weight are almost identical at about 31.1 g.
• A South African Krugerrand is 22 carat (91.67% gold). To hold one troy ounce of fine gold it weighs about 33.93 g, with copper making up the rest.

Worked example: 33.93 g x 0.9167 = 31.10 g of fine gold, which is one troy ounce. The extra 2.8 g of copper adds hardness, not value. Read more about purity in our entry on fineness and how alloys are expressed in carats.

Converting troy ounces to AUD prices

International spot prices are quoted in US dollars per troy ounce. Australian dealers convert that figure into AUD using the current exchange rate, so the Australian price can move even on a day when the US dollar gold price is flat. If you think in grams, divide the price per troy ounce by 31.1035, or use our gold price per gram in AUD. For larger holdings, the price per kilo is handy, since 1 kg cast bars are a common size in Australia.

Fractional coins are labelled in parts of a troy ounce: 1/2, 1/4, 1/10 and 1/20 oz. A 1/10 oz Kangaroo holds 3.11 g of gold, but its price per gram is usually higher than a 1 oz coin because minting costs are spread over less metal. That difference is the premium over spot, which we rank for every product in our list of the cheapest gold coins in Australia.