Gold Karat and Purity Explained

Gold purity is expressed in two ways. The karat system divides an item into 24 parts and counts how many are gold: 24 karat is pure, 18 karat is 18 parts gold and 6 parts other metal. The fineness or millesimal system counts parts per thousand: 750 means 750 parts of gold in 1,000.

The two are interchangeable. Divide the karat by 24 to get the fraction, multiply by 1,000 for fineness. 14 ÷ 24 = 0.583, yet 14k jewelry is usually stamped 585. The extra two thousandths are a manufacturing tolerance: makers alloy slightly above the legal minimum so a piece never tests under its mark.

These are the purities you will meet in practice, with their usual stamps and where they are used.

• 24k — 999 or 9999. Bullion bars, investment coins, Chinese and Thai pure-gold jewelry.
• 22k — 916. India, Pakistan, the Gulf, Singapore and Malaysia; also older British coins such as the Sovereign.
• 21k — 875. Egypt, Saudi Arabia, Jordan and much of the Middle East.
• 18k — 750. Italian, French and Swiss jewelry, luxury watches.
• 14k — 585. The most common jewelry alloy in the US, Germany, Scandinavia and Eastern Europe.
• 10k — 417. The legal minimum to be called gold in the United States.
• 9k — 375. The legal minimum in the UK, Ireland and Australia.

The world gold price is quoted for pure gold per troy ounce. Dividing by 31.1035 gives the price of one gram of pure gold. To value any other karat, multiply by its fineness.

Worked example: suppose pure gold is $4,200 per ounce. One gram of pure gold is $4,200 ÷ 31.1035 = $135.03. One gram of 22k is $135.03 × 0.916 = $123.69. One gram of 14k is $135.03 × 0.585 = $78.99. One gram of 9k is $135.03 × 0.375 = $50.64. The karat pages on this site run this calculation continuously with the live price.

This is why a heavy 9k chain can be worth less than a light 18k ring. Weight only matters once you know how much of it is gold.

Pure gold is very soft: you can mark 24k with a fingernail. Jewelers add silver, copper, zinc, nickel or palladium to make it harder and to change its colour. More copper gives rose gold; nickel or palladium give white gold, which is then usually plated with rhodium for a bright finish.

Colour does not change value. A white 14k ring and a yellow 14k ring contain the same 58.5% gold. The alloy metals themselves are worth very little and refiners do not pay for them.

Lower karats are harder. That is why American class rings are often 10k and why many people choose 14k for engagement rings worn every day. 18k has a richer colour and more gold per gram but scratches and bends faster. 22k and 24k jewelry is soft enough that intricate pieces can deform, which is one reason it is bought partly as savings rather than purely as decoration.

Because preferences differ so much between countries, the karat of a piece often tells you where it was made. A box of inherited jewelry in the UK is likely to be mostly 9k; in the US, 10k and 14k; in Italy, 18k; in India or Dubai, 22k. Knowing this helps you spot pieces that may be mis-sorted, and explains why buyers in some markets quote 21k or 22k per-gram prices every morning while others never mention them.

If you travel or buy online, remember that a 22k bangle bought in Dubai and a 22k bangle bought in Mumbai have the same gold content, but local taxes and making charges differ — compare the per-gram gold price, not the ticket price.

Stamps can be worn away or, rarely, faked. Buyers test with acid kits (scratch the item on a stone and apply acids of known strength), electronic conductivity testers, or X-ray fluorescence (XRF) machines, which read the surface alloy in seconds without damage. For plated items XRF reads the plating, so a buyer may file a small notch to check the base metal. Ask before they do.