The short answer
A troy ounce is the unit used to weigh and price gold, silver, platinum and palladium. It’s 31.103 grams, about 10% heavier than the ordinary ounce of 28.350 grams used for food and most other things. When you see a gold price per ounce, or a coin sold as 1 oz, it means a troy ounce.
At a glance
| 1 troy ounce | 31.103 grams, or 480 grains |
| 1 ordinary (avoirdupois) ounce | 28.350 grams, or 437.5 grains |
| Difference | A troy ounce is about 9.7% heavier |
| 1 kilogram | About 32.15 troy ounces |
| 1 troy pound | 12 troy ounces, or 373.24 grams |
Troy ounce vs. ordinary ounce
Both ounces are built from the same small unit, the grain, which is defined as exactly 64.79891 milligrams. A troy ounce is 480 grains. The ordinary ounce, which the U.S. uses for almost everything else and which is officially called the avoirdupois ounce, is 437.5 grains. That makes the troy ounce about 9.7% heavier.
Pounds work the other way round. A troy pound has 12 troy ounces and weighs 373.24 grams, while an ordinary pound has 16 ounces and weighs 453.59 grams. The metals trade rarely uses troy pounds today. Prices are quoted per troy ounce, per gram or per kilogram.
Why it matters when you buy or weigh metal
A kitchen or postal scale weighs in ordinary ounces, so precious metals look heavier on it than you might expect. A coin containing one troy ounce of pure gold, such as a Canadian Maple Leaf, shows about 1.10 ounces on an ordinary scale. An American Gold Eagle shows about 1.20 ounces, because it weighs 33.931 grams in total with the silver and copper mixed into its gold.
To check coins or bars, weigh them in grams, or set a digital scale to troy ounces if it has that mode (often shown as ozt).
The unit matters for prices too. The spot price of gold is quoted per troy ounce. To get the price per gram, divide by 31.103, so gold at $4,300 an ounce works out to about $138 a gram. Jewelry buyers sometimes quote per gram or per pennyweight instead, so convert offers into the same unit before comparing them.
Grams, kilos and other units you’ll see
Small gold bars are often sold in grams, and larger ones in kilos or troy ounces. Our guide to gold bars covers the common sizes. The jewelry trade also uses the pennyweight, which is one-twentieth of a troy ounce.
| Unit | Grams | Troy ounces |
|---|---|---|
| 1 grain | 0.0648 | 0.0021 |
| 1 gram | 1 | 0.0322 |
| 1 pennyweight (dwt) | 1.555 | 0.05 |
| 1 ordinary ounce | 28.350 | 0.9115 |
| 1 troy ounce | 31.103 | 1 |
| 1 troy pound | 373.24 | 12 |
| 1 ordinary pound | 453.59 | 14.58 |
| 1 kilogram | 1,000 | 32.15 |
Where the name comes from
The troy system has been used to weigh gold, silver and gemstones since the Middle Ages. Britannica says the name supposedly comes from Troyes, a French city that held one of the major medieval trade fairs. The U.S. Mint adopted the troy pound for regulating coinage in 1828, and the troy ounce is still the standard unit for precious metals, from coins to futures contracts.
Frequently asked questions
Is a troy ounce bigger than a regular ounce?
Yes. A troy ounce is 31.103 grams and a regular ounce is 28.350 grams, so the troy ounce is about 9.7% heavier.
How many grams are in a troy ounce?
31.103 grams, or exactly 31.1034768 grams.
How many troy ounces are in a kilogram?
About 32.15, which is why a kilo gold bar is priced at roughly 32 times the price per ounce.
Is a troy pound heavier than a regular pound?
No. A troy pound is 12 troy ounces, or 373.24 grams, while a regular pound is 453.59 grams.
Why is gold priced in troy ounces?
It’s the traditional unit for precious metals, and the markets still use it. A standard gold futures contract, for example, covers 100 troy ounces.