Troy Ounce Explained
Troy Ounce Weight and Definition
When you're looking at prices for gold, silver, platinum or palladium, you'll come across the troy ounce. It's a specific unit of weight, set at 31.1035 grams. That makes it heavier than the ounce you'd see on a kitchen scale or a grocery store shelf.
The troy system goes back centuries and was widely adopted for valuing precious metals in markets. Its connection to the French trading center Troyes is often cited, though not every historian agrees on the details. Today, the troy ounce remains the global reference for bullion trading.
If you see "troy" attached to an ounce, that refers only to the measurement, not the purity or value of the metal itself. A troy ounce of platinum is as heavy as a troy ounce of silver. Their worth, though, is entirely different.
Troy Ounce Compared With the Everyday Ounce
Most weighing at home or work is done using the avoirdupois ounce. That's the one on postal scales and food packaging, and it weighs around 28.35 grams. Compared to that, the troy ounce is roughly 10 percent heavier.
The pounds in these two systems aren't the same, either. There are 12 troy ounces in a troy pound (about 373 grams), but 16 avoirdupois ounces in a regular pound (about 454 grams). So, if you're looking at a figure in troy pounds, be careful: one troy pound doesn't match one regular pound, and a dozen troy ounces won't weigh the same as a pound of rice.
On price sheets, always check whether the weight is troy or avoirdupois. In bullion trading, "ounce" almost always means troy, though labels may switch to grams, especially for jewelry or coins sold by weight.
Why Precious Metals Are Still Quoted in Troy Ounces
The main reason gold and other precious metals stick with troy ounces is custom: that's how the market has priced transactions and set contracts for a very long time. If you changed the unit now, it would create confusion and break the link to historical data.
If you want to turn a price per troy ounce into a price per gram, divide by 31.1035. We lay out the detailed steps in our guide on calculating gold prices by gram. If you need to check what the spot price means, there's an explanation in the spot price guide.
Once you convert prices using the right rate, a troy ounce figure and a gram figure mean the same thing for the same metal. Be sure you know the unit before lining up quotes from different providers.
Frequently asked questions
How many grams are in a troy ounce?
There are exactly 31.1034768 grams in a troy ounce, and it's usually rounded to 31.1035 grams on market sheets. That makes the troy ounce about 1.097 times as heavy as the standard (avoirdupois) ounce, which is 28.35 grams. Pricing and conversion tools for precious metals rely on the 31.1035 gram figure for troy ounces.
Is a troy ounce the same as a regular ounce?
No. A troy ounce is about 31.1 grams; the "regular" avoirdupois ounce used for most goods is near 28.3 grams. The troy ounce is for gold, silver, and similar metals, not groceries or letters. Always look up the unit name before you compare prices or make a transaction.