Karat to percent
Divide the karat by 24. Gold sold in the UK is hallmarked with a fineness number instead, in parts per thousand.
| Karat | Gold content | UK fineness mark |
|---|---|---|
| 24k | 100% (99.9% in practice) | 999 |
| 22k | 91.7% | 916 |
| 18k | 75% | 750 |
| 14k | 58.3% | 585 |
| 10k | 41.7% | none |
| 9k | 37.5% | 375 |
The rest is other metals, which make the gold harder and change its colour. 10k is common in the US but isn’t a UK hallmark standard; the lowest UK gold standard is 375 (9 carat).
Gold in a piece
Multiply the weight by the karat ÷ 24. An 18k ring weighing 5 g contains 5 × 18 ÷ 24 = 3.75 g of gold.
Not the same as carat
In the US, karat with a K measures gold purity and carat with a C measures the weight of gemstones. In the UK both are spelled “carat”, so 18 carat gold is written 18ct. Read the context.