Conversion table
| Carat | Fineness mark | Gold content | Fine gold in 10 g | Typical use |
|---|---|---|---|---|
| 9ct | 375 | 37.5% | 3.75 g | Most British high street jewellery |
| 14ct | 585 | 58.5% | 5.85 g | US and European jewellery |
| 18ct | 750 | 75.0% | 7.50 g | British fine jewellery, engagement rings |
| 22ct | 916 | 91.6% | 9.16 g | South Asian jewellery, gold sovereigns |
| 24ct | 999 / 999.9 | 99.9% + | 9.99 g | Investment bars, bullion coins |
How to use it
Weigh the item in grams, find its standard from the fineness mark, then multiply. A 34 gram 916 bangle contains 34 × 0.916 = 31.14 grams of fine gold. Do this separately for each standard: never average a mixed lot.
Carat, karat and fineness
"Carat" spelled with a c is the purity measure for gold in Britain; "karat" is the American spelling of the same thing. Carat with a c also describes the weight of a gemstone, which is an entirely different measure — a source of regular confusion when a ring has both.
Why the figures are not exact fractions
14ct is arithmetically 58.33% and 22ct is 91.67%, but the marks read 585 and 916. Fineness standards are set as guaranteed minimums, so manufacturers alloy slightly above the arithmetic figure to be certain of meeting them.
Standards outside the table
| Mark | Carat | Gold content | Where it turns up |
|---|---|---|---|
| 417 | 10ct | 41.7% | United States |
| 500 | 12ct | 50.0% | British and European pieces made before 1932 |
| 625 | 15ct | 62.5% | British jewellery made before 1932 |
| 833 | 20ct | 83.3% | South Asian and Middle Eastern jewellery |
| 875 | 21ct | 87.5% | Middle Eastern jewellery |
Only 375, 585, 750, 916 and 999 may be struck as gold fineness marks on a current UK hallmark. The rest are foreign standards or historic British ones — 12ct and 15ct were withdrawn in 1932 and replaced by 14ct. All of them are valued the same way: fineness multiplied by weight.
A worked example
A drawer holds 18.4 grams of 9ct chain, a 4.2 gram 18ct ring and an 11.6 gram 22ct bangle. Fine gold content is (18.4 × 0.375) + (4.2 × 0.75) + (11.6 × 0.916), which is 6.90 + 3.15 + 10.63 = 20.68 grams. The bangle is barely a third of the weight but holds half the gold — the reason mixed lots are never averaged.
Related conversions
For weight units, see grams versus troy ounces. To do the arithmetic automatically, use the gold purity conversion chart.
