Troy Ounce vs Ounce: What's the Difference?
If you're buying or selling gold or silver, you need to know the difference. It's about 10% of your money.
The Quick Answer
A troy ounce weighs 31.1035 grams. A regular (avoirdupois) ounce weighs 28.3495 grams. A troy ounce is about 10% heavier than a standard ounce.
When you see gold or silver prices quoted "per ounce," they always mean troy ounces. When you step on a bathroom scale or buy food at the grocery store, those are standard ounces. Mixing up the two when buying or selling precious metals means a 10% pricing error.
Why Do Precious Metals Use Troy Ounces?
The troy weight system dates back to medieval markets in Troyes, France, where traders established standardized weights for precious metals. The system predates the avoirdupois system used for everyday goods and has been the global standard for gold and silver trading for centuries.
The troy system was adopted by the US Mint when it was established in 1792 and remains the standard today. Every gold bar, silver coin, and platinum piece you encounter is weighed in troy ounces.
Conversion Reference
| Measurement | Troy Ounce | Standard (Avoirdupois) Ounce |
|---|---|---|
| Grams | 31.1035 g | 28.3495 g |
| Grains | 480 grains | 437.5 grains |
| Pennyweights | 20 dwt | 18.23 dwt |
| Ounces per pound | 12 troy oz = 1 troy pound | 16 oz = 1 standard pound |
| Grams per pound | 373.24 g (troy pound) | 453.59 g (standard pound) |
Important: A troy pound contains only 12 troy ounces, not 16. So while a troy ounce is heavier than a standard ounce, a troy pound is actually lighter than a standard pound. This confuses people, but in practice you'll almost never encounter "troy pounds." Precious metals are quoted per troy ounce.
What This Means When You're Selling
If someone offers to buy your gold "per ounce" without specifying troy ounces, make sure you're speaking the same language. Gold priced at $5,000 per troy ounce is about $5,000 per 31.1 grams. If a buyer is weighing your gold on a standard kitchen scale and quoting "per ounce," you could be underpaid by roughly 10%.
Reputable precious metals buyers like US Gold & Coin always weigh items on calibrated troy scales and quote prices in troy ounces. If any buyer can't explain the difference between troy and standard ounces, that's a red flag.
Common Conversions
| If you have... | That's approximately... |
|---|---|
| 1 troy ounce of gold | 31.1 grams |
| 1 troy ounce of silver | 31.1 grams |
| 1 gram of gold | 0.03215 troy ounces |
| 10 grams of gold | 0.3215 troy ounces |
| 100 grams of silver | 3.215 troy ounces |
| 1 kilogram of gold | 32.15 troy ounces |
What's Your Gold or Silver Worth?
Wondering what your gold or silver is worth at current troy ounce prices? US Gold & Coin offers free appraisals and pays based on accurate troy weights. Call 888-284-6120 or visit any of our locations.
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See also: Selling Guide · Inherited Coin Collection Guide