Lesson 2 of 4 · 4 min read
Ounces, grams and karats
The troy ounce, the gram and the tola, and how karats and fineness tell you how much gold you really have.
Wherever you buy gold you will meet two measures: how much it weighs, and how pure it is.
The troy ounce is not a normal ounce
Gold is weighed in troy ounces. One troy ounce is 31.1035 grams, about 10% more than the ordinary ounce used for food, which is 28.35 grams. When you see a price per ounce for gold, it always means a troy ounce.
| Unit | Grams | Where you will see it |
|---|---|---|
| Troy ounce | 31.1035 | Global prices, coins, bars |
| Gram | 1 | Jewellery and small bars in most of the world |
| Kilogram | 1,000 (32.15 troy ounces) | Large bars, central banks |
| Tola | 11.6638 | India, Pakistan and the Gulf |
Karats measure purity
Pure gold is soft, so most jewellery is mixed with other metals such as silver, copper or zinc to make it harder. Purity is measured in karats out of 24, or as fineness in parts per thousand, which is often stamped on the item.
- 24 karat is 99.9% gold, stamped 999. Bars and many coins.
- 22 karat is 91.6% gold, stamped 916. Common for jewellery in India, Nigeria and the Gulf.
- 21 karat is 87.5% gold, stamped 875. Popular in the Middle East.
- 18 karat is 75% gold, stamped 750.
- 14 karat is 58.5% gold, stamped 585.
- 9 karat is 37.5% gold, stamped 375.
So a 10 gram chain at 18 karats contains 7.5 grams of pure gold. Here is what a gram of each purity is worth at today's price:
| Karat | Gold content | Per gram |
|---|---|---|
| 24K | 99.9% · 999 | |
| 22K | 91.6% · 916 | |
| 21K | 87.5% · 875 | |
| 18K | 75.0% · 750 | |
| 14K | 58.5% · 585 | |
| 9K | 37.5% · 375 |
Why this matters
A seller who quotes a price "per gram" may mean grams of 22 karat jewellery, not pure gold. Always ask two questions: how many grams, and what karat. Then you can work out the pure gold content and compare the price with the spot price, which Buying gold safely shows you how to do.
Something not clear? Ask about it in plain language.
Check what you learned
3 quick questions. Pick an answer to see why.
TGM Academy is education, not financial advice. Past results are not a guide to future returns.