What Do 24K, 22K and 999.9 Mean? A Simple Guide to Gold Purity

Gold purity is measured in two main ways: carats (written as K or ct) and fineness (written as a number such as 999.9). Pure gold is 24 carat, or 999.9 fine. Lower carat numbers mean the gold is mixed with other metals to make it harder, change its colour or lower its price. Knowing how to read these marks helps you understand exactly what you are buying, whether it is a ring, a chain or a coin.

What does carat mean?

The carat system divides gold into 24 parts. A piece marked 24K is made entirely of gold, while an 18K piece is 18 parts gold and 6 parts other metals. Here are the most common carat grades:

• 24K: about 99.9% gold. Very soft and rich yellow in colour.
• 22K: about 91.7% gold. Popular for traditional jewellery and some well-known coins.
• 18K: 75% gold. A favourite for fine jewellery because it balances colour and strength.
• 14K: about 58.5% gold. Common in the United States for everyday jewellery.
• 9K: 37.5% gold. Widely sold in the UK as an affordable option.

What does fineness mean?

Fineness shows purity in parts per thousand. A mark of 750 means 750 parts out of 1,000 are gold, which is the same as 18 carat. Coins and bars often show fineness instead of carats:

• 999.9: sometimes called “four nines”, this is 99.99% pure gold, used for coins such as the Canadian Maple Leaf and the modern Britannia.
• 999: 99.9% pure gold.
• 916.7: 22 carat, used for coins such as the Krugerrand and the American Gold Eagle.
• 585 and 375: 14 and 9 carat jewellery.

Why is some gold mixed with other metals?

Pure gold is beautiful but soft, so it scratches and bends easily. Jewellers add metals such as copper, silver, zinc or palladium to make it tougher. These alloys also change the colour. Copper gives rose gold its warm pink tone, while white gold usually contains palladium or nickel and is often plated with rhodium for a bright finish.

Why some coins are 22 carat

Coins such as the Krugerrand and the American Gold Eagle are struck in 22 carat gold. They still contain a full troy ounce of pure gold, but the extra alloy makes them heavier and more resistant to scratches. Other coins, such as the Maple Leaf and the Britannia, are struck in 24 carat gold for maximum purity. Both approaches are common, and the choice is mostly a matter of preference.

How to read hallmarks

In many countries, gold items must carry an official hallmark to prove their purity. In the UK, hallmarks are applied by independent assay offices in London, Birmingham, Sheffield and Edinburgh. A typical UK hallmark includes:

• The sponsor’s mark, showing who made or sent the item for testing.
• The fineness mark, such as 375, 585, 750 or 916.
• The assay office mark, such as a leopard’s head for London.
• An optional date letter showing the year of hallmarking.

Other countries use their own systems, but the fineness number is usually easy to spot.

A short history of gold purity marks

Hallmarking is one of the oldest forms of consumer protection. In England, the practice dates back to 1300, when a law required gold and silver to be tested before sale. The word “hallmark” comes from Goldsmiths’ Hall in London, where items were assayed and stamped. Today, the system still protects buyers by confirming that an item contains the gold it claims to.

The word “carat” has an older origin. It is thought to come from the carob seed, which was once used as a small standard weight by traders. Over time, the term came to describe the purity of gold, while “carat” for gemstones still refers to weight.

Which purity should you choose?

For jewellery you wear every day, such as a wedding ring, 18K or 14K offers a good balance of colour and durability. For special pieces that you wear less often, 22K gives a rich, traditional look. For coins and bars, both 22K and 24K are widely accepted, so you can simply choose the design you like best.

Tips for buying gold with confidence

• Look for clear hallmarks or official mint markings.
• Ask the seller to state the carat or fineness in writing.
• Be cautious of very low prices for high-carat items.
• Buy coins and bars from established mints and recognised dealers.

If you are curious to see purity marks on real products, dealers such as Bitgolder list coins and bars with their fineness and weight clearly shown, which is a handy way to learn how these marks appear in practice.

Frequently asked questions

Is 24K gold the best choice for jewellery?

Not always. It is the purest, but it is also the softest, so it can scratch and bend more easily. Many people prefer 18K or 14K for everyday pieces.

Is 22K gold real gold?

Yes. It is about 91.7% gold, and the rest is a small amount of other metals that make it stronger.

What does 750 mean on a ring?

It means the ring is 75% gold, which is the same as 18 carat.

Does white gold contain real gold?

Yes. White gold is real gold mixed with white metals such as palladium, and it is often plated with rhodium for extra shine.

Why does gold jewellery look different colours?

The colour depends on which metals are mixed with the gold. More copper creates a rose tone, while palladium or nickel creates white gold.

How can I tell if gold is real at home?

Check for hallmarks first. Simple home tests, such as using a magnet, can rule out some fakes because gold is not magnetic, but only a professional test can confirm purity.

The bottom line

Carats and fineness numbers tell you how much gold is in what you buy. Once you know that 24K and 999.9 mean pure gold, and that lower numbers mean stronger alloys, choosing jewellery, coins or bars becomes much easier.