Gold purity is measured in carats, out of 24. 24 carat is pure gold; 18 carat is 18 parts gold in 24, or 75% gold, stamped 750; 14 carat is 58.5% gold, stamped 585; and 9 carat is 37.5% gold, stamped 375. The rest is other metals such as silver, copper, zinc or palladium, which make the gold harder and change its colour. In the UK the number is part of the hallmark.
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Gold carats and hallmark numbers
- 9 carat
- Hallmark number
- 375
- Pure gold
- 37.5%
- Notes
- The lowest standard that can be hallmarked as gold in the UK
- 14 carat
- Hallmark number
- 585
- Pure gold
- 58.5%
- Notes
- Common in the US and Europe
- 18 carat
- Hallmark number
- 750
- Pure gold
- 75%
- Notes
- The usual standard for fine jewellery and watches
- 22 carat
- Hallmark number
- 916
- Pure gold
- 91.6%
- Notes
- Rich yellow; wedding rings, sovereigns, Asian gold
- 24 carat
- Hallmark number
- 999 or 990
- Pure gold
- 99.9% or 99%
- Notes
- Pure gold; bullion bars and coins
So the "18 carat gold number" is 750, and 18 carat gold is 75% pure gold.
Carat and karat
Carat is the British spelling, karat the American, and "K" or "KT" is used in stamps such as 18K. Do not confuse it with the carat used to weigh gemstones: a 1 carat diamond has nothing to do with gold purity.
9KT gold
9 carat gold is 37.5% gold and 62.5% other metals, usually silver and copper. It is hard-wearing and the most common gold standard in British jewellery, from chains and lockets to signet rings. 9 carat became a legal standard in Britain in 1854.
14KT gold
14 carat gold is 58.5% gold. It is the most popular standard in the United States and common in continental Europe. In Britain it replaced the old 12 and 15 carat standards in 1932.
18KT gold
18 carat gold is 75% gold. It has a rich colour and is the usual standard for fine jewellery, engagement rings, designer pieces and gold watches. Cartier, Van Cleef & Arpels and most Swiss watchmakers use 750 gold.
22KT and 24KT gold
22 carat gold, 91.6% gold, is soft and deep yellow. It is used for wedding rings, for gold sovereigns and widely in South Asian and Middle Eastern jewellery. 24 carat gold is pure and too soft for most jewellery; it is used for bullion bars and coins.
Purity, colour and durability
- Higher carat, softer metal. 22 and 24 carat scratch and bend more easily; 9 and 14 carat are harder.
- Colour. The alloy decides the colour: copper for rose gold, silver for greener yellow, and palladium or nickel for white gold, which is usually rhodium plated.
- Skin. Higher carat gold contains less of the other metals that can irritate sensitive skin.
How carats help date old gold
British gold standards changed over time, so the carat can help date a piece:
- 22 carat has been a British standard for centuries; 18 carat from 1798.
- 15, 12 and 9 carat were introduced in 1854.
- 15 and 12 carat were replaced by 14 carat in 1932.
A 15 carat Victorian locket, for example, must date from between 1854 and 1932.
How to read the purity of your gold
0 of 4 checked
1Look for the number
Look for the number inside rings, on clasps and on the backs of pendants: 375, 585, 750, 916 or 999.
2Look for a full UK hallmark
Look for a full UK hallmark: maker’s mark, fineness number, assay office mark and usually a date letter.
3Older British gold
Older British gold may show the carat in figures, such as 18 or 15, with a crown.
4Plating marks
Plating marks such as GP, GF or 18K GE mean plated, not solid gold.
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What makes gold jewellery valuable?
The carat and the marks come first, then the maker or designer, the age and style, any gemstones, the condition and any box or papers. We never publish figures; every piece is different.
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- Carat and marks
- Maker
- Age and style
- Gemstones
- Condition
- Box and papers
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Questions people ask
How much gold is in 18 carat gold?
75%. 18 carat gold is 18 parts pure gold out of 24, stamped 750.
What is the hallmark number for 18 carat gold?
750, meaning 750 parts of gold per thousand.
What does 9KT gold mean?
37.5% pure gold, stamped 375. The rest is other metals, usually silver and copper.
What is the purity of 14KT gold?
58.5% gold, stamped 585.
Is 24 carat gold pure?
Yes. 24 carat is pure gold, stamped 999 or 990.
Which is better, 9KT or 18KT gold?
They suit different uses. 18 carat has more gold and a richer colour; 9 carat is harder-wearing. Both are genuine gold when hallmarked.
Related guides
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