One troy ounce of gold weighs 31.1035 grams, about 10% heavier than the 28.35-gram avoirdupois (regular) ounce. So how many grams in an ounce of gold? The gold market answer is 31.1035 grams, because gold trades in troy ounces, not the everyday ounce you use in the kitchen. This article shows you how to convert between grams and troy ounces for the coin and bar sizes you can buy.
Key takeaways
- One troy ounce of gold weighs 31.1035 grams, the standard the gold market uses.
- Gold, silver, and platinum are weighed in troy ounces, not the everyday ounce used for food and household goods.
- Knowing the troy conversion lets you compare coin and bar sizes by exact weight.
Troy ounce vs regular ounce
Here’s how the two measurements compare:
| Ounce type | Weight in grams | Where it’s used |
|---|---|---|
| Troy ounce (gold standard) | 31.1035 g | Gold, silver, and platinum |
| Avoirdupois (regular) ounce | 28.35 g | Food and everyday goods |
Gold measured in troy ounces explained
The troy ounce is the gold industry standard for weight. The system dates back to medieval Europe, and even as other measurements changed over the centuries, the troy ounce stayed the way gold is weighed today.
Calculating grams in a troy ounce
Since the gold market doesn’t use the standard ounce, how do you calculate the grams in any gold piece you’re looking at? Here’s how:
- If you see troy ounces: Multiply the troy ounce amount by 31.1035 to get the weight in grams.
- If you see grams: Multiply the grams by 0.03215 to get the troy ounces.
Swiss America’s 2025 sales data shows that 39.5% of investors buy gold in the 0.5 to 1 oz range, so these conversions come up often when comparing weights. Here are a few examples:
- 0.5 troy oz: 0.5 × 31.1035 = 15.55175 grams
- 10 grams: 10 ÷ 31.1035 = 0.3215 troy oz
- 1/10 oz: 0.1 × 31.1035 = 3.11035 grams
Here’s a table to easily see the difference:
| Weight shown | Conversion formula | Result |
|---|---|---|
| 1 gram | 1 ÷ 31.1035 | 0.03215 troy oz |
| 2.5 grams | 2.5 ÷ 31.1035 | 0.08037 troy oz |
| 5 grams | 5 ÷ 31.1035 | 0.16075 troy oz |
| 10 grams | 10 ÷ 31.1035 | 0.3215 troy oz |
| 20 grams | 20 ÷ 31.1035 | 0.643 troy oz |
| 50 grams | 50 ÷ 31.1035 | 1.6075 troy oz |
| 1/4 troy oz | 0.25 × 31.1035 | 7.7759 grams |
| 1/2 troy oz | 0.5 × 31.1035 | 15.55175 grams |
| 1 troy oz | 1 × 31.1035 | 31.1035 grams |
Gold weights for coins and bars
You don’t always have to buy one troy ounce of gold. You can buy gold coins or bars in smaller sizes, too. The size you choose affects price and premiums. Common gold bar weights you’ll see include:
1 gram, 5 grams, 10 grams, 20 grams, 1 troy ounce, 50 grams, 100 grams, 250 grams, 500 grams, and 1 kilogram.
And you can buy gold coins in these fractional sizes: 1 ounce, 1/2 ounce, 1/4 ounce, and 1/10 ounce.
Gold purity measurements
Besides how much they weigh, gold and other precious metals are also measured by their purity levels:
- 99.99%: Known as four nines fine. You’ll see it in products like the Canadian Gold Maple Leaf, Australian Kangaroo, and many PAMP Suisse and Valcambi bars.
- 99.9%: Also known as three nines fine. Some international bullion bars and coins carry this purity, including certain products from the Royal Mint and the Austrian Mint.
- 99.5%: The minimum purity required for IRA-approved gold bars. You’ll see it in bars from refiners accredited by LBMA, like Metalor or Argor Heraeus.
- 91.67%: Purity of the American Gold Eagle. It’s a 22-karat coin, but it still contains one full troy ounce of pure gold, with small amounts of silver and copper added for durability.
The gold standard and market
The United States once followed the gold standard, which meant the U.S. dollar was backed by gold. President Roosevelt ended it domestically in 1933 with Executive Order 6102 and the Gold Reserve Act, which restricted private gold ownership. President Nixon ended it internationally in 1971.
Ever since these changes, gold’s value has been driven by supply and demand. Because it’s an independent asset, investors use it to diversify their portfolios. Here are some of the other benefits of owning gold:
- Inflation protection: When prices rise and the dollar weakens, gold tends to hold its buying power. That’s why investors buy more during inflationary periods.
- Portfolio diversification: Gold doesn’t follow the stock market, so it gives you a separate asset to balance volatility in your other holdings.
- Store of value: Gold has carried its value through every major economic cycle, which makes it a reliable way to preserve wealth over time.
- No counterparty risk: Gold is an independent tangible asset. It doesn’t depend on a company staying profitable or a financial system staying stable.
Other precious metals
Besides gold, other metals that also use the troy system are:
- Silver: Lower cost per ounce, strong industrial demand, and an easier entry point for new investors. Silver carries more price volatility than gold and is bulkier to store in larger amounts.
- Platinum: Rarer than gold and used in automotive and industrial applications, with potential upside when supply tightens. It is more volatile than gold because prices shift with industrial demand.
- Palladium: High demand in catalytic converters, limited global supply, and strong performance in certain cycles. It is the most volatile of the precious metals due to tight supply and heavy reliance on specific industries.
Final thoughts on gold measurement
The troy ounce governs every gold coin and bar you buy, so the 31.1035 gram conversion is worth keeping handy when you compare sizes and prices.
If you want to learn more about gold investing and the various weight options available, connect with the Swiss America team today!
How many grams in an ounce of gold: FAQs
How many grams in a troy ounce of gold?
One troy ounce of gold weighs 31.1035 grams. That is the weight used for every gold coin and bar on the market, from a 1/10 ounce coin to a 400 ounce bar. A regular ounce, by contrast, is 28.35 grams.
Is an ounce 28 or 32 grams of gold?
An ounce of gold isn’t 28 or 32 grams. Gold uses the troy ounce, which is 31.1035 grams. That’s the standard the entire precious metals market relies on.
How many grams are in an ounce of gold 14K?
A 14K gold ounce weighs 31.1035 grams. The weight doesn’t change. What changes is the purity. Fourteen karat gold is 58.3% pure gold, with the rest made up of other metals.
Is it legal to own a 400 oz gold bar?
Yes, it is legal to own a 400 oz gold bar. A bar that size weighs about 27.4 pounds, and at current prices it runs well into six figures. That is why most investors choose smaller bars or coins that are easier to store, insure, and sell.
The information in this post is for informational purposes only and should not be considered tax or legal advice. Please consult with your own tax professionals before making any decisions or taking action based on this information.
