Gold karats and purity explained

Karats, carats and millesimal fineness

Gold purity is described in two systems that mean the same thing. The karat system divides the metal into 24 parts: 24 karat is (practically) pure gold, 18 karat is 18 parts gold and 6 parts other metals, and so on. In British English the word is usually spelled carat, which confuses it with the carat used to weigh gemstones — the two units are unrelated.

The millesimal system, used on most European hallmarks, gives the number of parts of pure gold per thousand. 750 means 750 parts in 1,000, which is 75%, identical to 18 karat. Because 24 does not divide neatly into 1,000, the conversions are rounded: 14 karat is 58.33% in theory, but the legal standard and hallmark is 585, slightly higher, to make sure the item is never under-gold.

Conversion table

Here is how the common standards line up, with where you usually meet them:

• 24k = 999 (99.9%) — bullion bars and coins, traditional Chinese and Thai jewellery.
• 22k = 916 (91.6%) — Indian and Gulf jewellery, British sovereigns, Krugerrands, wedding bands.
• 21k = 875 (87.5%) — Middle East and North Africa.
• 18k = 750 (75%) — French, Italian, Spanish and Portuguese jewellery, most engagement rings.
• 14k = 585 (58.5%) — Germany, Poland, Scandinavia, the Baltics and much US jewellery.
• 10k = 417 (41.7%) — the minimum standard for 'gold' in the United States.
• 9k = 375 (37.5%) — the most common standard in the UK and Ireland.
• 8k = 333 (33.3%) — the lowest legal gold standard in Germany and Greece.

Why jewellery is not pure gold

Pure gold is very soft. A 24 karat ring scratches and bends easily, and it cannot hold a stone securely. Alloying gold with silver, copper, zinc, nickel or palladium makes it harder and changes its colour. Copper produces rose and red gold; silver and a little copper give classic yellow; palladium or nickel produce white gold, which is then usually plated with rhodium for a bright finish.

Colour does not change the value of the gold content. An 18 karat white gold ring and an 18 karat yellow gold ring of the same weight contain the same amount of gold and have the same melt value. The alloying metals themselves are worth very little and are ignored in scrap valuations.

How purity affects the gold price per gram

Since the price of gold is quoted for pure metal, the price of any karat is simply the pure gold price multiplied by its fineness. If pure gold is 100 per gram, 18 karat is worth 75, 14 karat 58.50 and 9 karat 37.50. This is why a heavy 9 carat chain can be worth less than a light 18 carat ring.

Our karat price table does this calculation with the live price for every standard, and each karat has a dedicated page with a calculator: 24k, 22k, 18k, 14k and 9k.

Choosing a karat when buying

Higher karats look richer and are more resistant to tarnish, but they are softer and more expensive. 18 karat is the common compromise for fine jewellery in continental Europe. 14 karat is harder, cheaper and very popular for everyday rings and chains. 9 karat is the most affordable and most durable, but its colour is paler and it can tarnish slightly over decades because of its high copper and silver content. 22 karat is favoured where gold jewellery is also a store of wealth, because its value is closer to that of pure gold.

If resale value matters to you, remember that jewellery is sold at retail prices that include design, labour, VAT and margin, but bought back on metal value only. A new 18 karat ring may cost two or three times its melt value. Bullion coins and bars are much closer to melt value in both directions — see gold vs silver for a comparison of the two main investment metals.

How purity is verified

In the UK, hallmarking is compulsory above set weight thresholds and is carried out by four independent Assay Offices. Many EU countries have similar state assay systems, and members of the Vienna Convention apply a Common Control Mark that is recognised across signatory countries. In countries without compulsory hallmarking, the mark is applied by the manufacturer and is a claim rather than an independent guarantee.

When you sell, a buyer will verify purity regardless of the stamp, using acid tests or an X-ray fluorescence (XRF) analyser. XRF is quick and non-destructive and gives a reading to one decimal place. Fire assay, the laboratory reference method, is used by refiners on melted bars. Our hallmark guide explains what each mark means in practice.

Unusual standards you may come across

Portuguese jewellery is often 19.2 karat (800). Older Russian and Soviet pieces use the zolotnik system: 56 zolotnik is roughly 14 karat (583) and 72 zolotnik roughly 18 karat. Some old American pieces are marked 12K or 15K, and Victorian British jewellery can be 15 carat (625) or 12 carat (500), standards abolished in 1932. All of these can be valued with the calculator by choosing the matching fineness.