One troy ounce of gold equals 31.1034768 grams, usually rounded to 31.1 grams. If you are wondering how many grams in an ounce of gold, this is the figure to use for gold bars, coins, and other precious metals sold by troy weight.
The confusion comes from the word “ounce.” A regular avoirdupois ounce weighs 28.35 grams, so it is lighter than a troy ounce. Using the wrong measurement can affect how you compare gold weights and prices.
Knowing the difference makes it easier to understand gold listings, convert between grams and troy ounces, and check whether a quoted weight matches the product. The sections below explain the troy ounce, show a practical conversion chart, and clear up how gold purity affects the amount of fine gold in an item.
Troy Ounce vs. Standard Ounce: Why the Difference Matters
What Is a Troy Ounce?
A troy ounce is the unit used to weigh precious metals such as gold and silver. One troy ounce equals exactly 31.1034768 grams.
When a gold bar or coin is described as weighing 1 oz, it normally means 1 troy ounce, not the ounce used for everyday household goods. That distinction is easy to miss if you are used to buying products measured in regular ounces.
What Is a Standard (Avoirdupois) Ounce?
A standard ounce, also called an avoirdupois ounce, is the unit commonly used for everyday products in countries that use the imperial or US customary measurement systems.
One avoirdupois ounce equals 28.349523125 grams, usually rounded to 28.35 grams.
That means a troy ounce contains more mass than a regular ounce. The two units have different definitions, even though both are called ounces.
Why the Mix-Up Costs You
A troy ounce is roughly 9.7% heavier than a standard ounce, at 31.1 grams compared with 28.35 grams. Using the wrong ounce when checking a gold item’s weight can lead to incorrect calculations when you compare its weight with a quoted gold price.
Why Is Gold Measured in Troy Ounces?
Rooted in medieval commerce, the troy weight system derives its name from Troyes, a French trading hub that established standardized weight units for precious metals centuries ago.
The system continued to be used for precious metals because traders needed consistent units when weighing and pricing valuable materials. Today, the troy ounce remains the standard unit for gold and other major precious metals in international markets.
Gold can also be measured in grams and kilograms, especially when dealing with gold jewellery or larger bars. But when you see an international gold price quoted per ounce, the ounce means a troy ounce.
Gold Weight Conversion Chart
Use this gold weight conversion chart to compare common weights. The figures are based on 1 troy ounce = 31.1034768 grams.
| Gold Weight | Grams (g) | Troy Ounces (oz t) |
|---|---|---|
| 1/10 oz t | 3.11 g | 0.10 oz t |
| 1/4 oz t | 7.78 g | 0.25 oz t |
| 1/2 oz t | 15.55 g | 0.50 oz t |
| 1 oz t | 31.10 g | 1.00 oz t |
| 2 oz t | 62.21 g | 2.00 oz t |
| 5 oz t | 155.52 g | 5.00 oz t |
| 10 oz t | 311.03 g | 10.00 oz t |
| 20 oz t | 622.07 g | 20.00 oz t |
| 1 kg | 1,000.00 g | 32.15 oz t |
For a troy ounce to grams conversion, multiply the number of troy ounces by 31.1034768. For example, a 5 oz gold bar weighs about 155.52 grams.
Does Gold Purity (Karat) Change the Weight?
Karat measures the purity of gold. It does not change the definition of a troy ounce.
A 1 oz item made from 24K gold weighs 31.1 grams if its stated weight is one troy ounce. An 18K gold item weighing one troy ounce also has a total weight of 31.1 grams. The difference is how much of that weight is pure gold.
- 24K gold: Usually about 99.9% pure gold. A 31.1 g item contains about 31.1 g of fine gold, depending on its stated fineness.
- 18K gold: 75% gold and 25% other metals. A 31.1 g item contains about 23.33 g of pure gold, with the remaining 7.77 g coming from alloy metals.
So, if you ask how many grams of 18K gold are in an ounce, the answer depends on whether you mean the total item weight or the amount of pure gold. The total weight is 31.1 grams, while the fine-gold content is about 23.33 grams.
Grams vs. Ounces in Gold Pricing
International gold prices are generally quoted per troy ounce, while some jewellers and gold buyers use a price per gram.
You can convert a price per troy ounce into a price per gram by dividing it by 31.1034768, or by 31.1 for a quick calculation.
For example, if gold is quoted at $3,100 per troy ounce, dividing $3,100 by 31.1 gives roughly $99.68 per gram.
This calculation gives you a simple way to compare prices quoted using different weight units. It does not account for dealer premiums, making charges, taxes, refining fees, or other costs that may apply to a particular gold product.
Other Gold Weight Units You May See
Gold is sometimes described using units other than grams and troy ounces, especially in jewellery and regional markets.
- Pennyweight (dwt): One pennyweight equals about 1.555 grams, or 1/20 of a troy ounce. It is commonly used in North American jewellery.
- Grain (gr): One grain equals about 0.0648 grams. It is a small traditional unit of mass.
- Tola: One tola is about 11.66 grams. It is widely used for gold in parts of South Asia.
- Tael: A tael is a traditional East Asian weight unit. Its exact value varies by region, with one commonly used bullion tael being about 37.42 grams.
These units can appear on older jewellery, bullion products, or price listings, so checking the unit before comparing weights is important.
FAQ
How much does an ounce of gold weigh?
A troy ounce of gold weighs exactly 31.1034768 grams, normally rounded to 31.1 grams. It is heavier than a regular avoirdupois ounce, which weighs 28.35 grams. When a gold product is listed as 1 oz, the weight generally refers to one troy ounce.
How many grams is 1 oz of gold?
One troy ounce of gold weighs 31.1034768 grams (commonly rounded to 31.1 g). Unlike everyday consumer items weighed in standard avoirdupois ounces (28.35 g), precious metals rely exclusively on troy ounces.
How many grams of 18K gold are in an ounce?
A 1 troy ounce piece of 18K gold weighs 31.1 grams in total. Since 18K gold is 75% pure, about 23.33 grams of that weight is pure gold. The remaining 7.77 grams consists of other metals used in the alloy.
How many grams are in a kilo of gold?
One kilogram contains 1,000 grams. Since one troy ounce equals 31.1034768 grams, a 1 kg gold bar contains about 32.15 troy ounces.
