What Does Carat Mean for Gold? Carat vs Karat Explained

For gold, carat measures purity. It tells you how many parts out of 24 are pure gold, with the rest made up of other metals alloyed in for strength and colour. So 24 carat gold is pure gold, 18 carat is 18 parts gold and 6 parts alloy (75% pure), and 9 carat is 9 parts gold and 15 parts alloy (37.5% pure). The higher the carat, the more actual gold you are wearing.

This trips people up because carat means something completely different for diamonds. A diamond carat is a unit of weight: exactly 0.2 grams. Gold carat has nothing to do with weight. A heavy 9ct chain contains less pure gold per gram than a light 18ct ring, and neither number tells you what either piece weighs. Same word, two unrelated measurements, and jewellers use both in the same sentence when describing a ring.

They are the same measurement with two spellings, split by geography. Karat with a K is the American spelling for gold purity, which is why you see 14k and 18k stamped on US-made jewellery. Carat with a C is the British and Australian spelling, usually abbreviated ct, which is why Australian jewellery reads 9ct or 18ct. An 18k ring and an 18ct ring have identical gold content.

The one place the spellings genuinely divide is gemstones. Diamond weight is always carat, never karat, in every country. So in American usage the split is tidy: karat for gold purity, carat for stone weight. In Australia we use carat for both and let context sort it out, which is exactly why the question gets asked. Our glossary has short entries for both carat and karat if you want the one-paragraph versions.

Every common carat, what it actually contains, and the number stamped inside the piece:

The three-digit hallmark is just the purity written as parts per thousand, so 750 means 750 parts gold in 1,000, which is 18ct. If the number inside your ring does not appear in this table, or you see letters like GP or GF instead, the piece may be plated rather than solid; how to test gold at home walks through reading hallmarks and confirming what you have.

Higher carat means more gold, not better jewellery. Purity buys you richer colour and more intrinsic metal value, and it costs you hardness. Pure gold is soft enough to mark with a fingernail press, which is why 24ct is the domain of bullion bars and ceremonial pieces rather than engagement rings. Alloying gold with copper, silver, palladium and zinc is what makes it survive daily wear.

The practical sweet spots for rings are 14k and 18ct. 14k (58.3% gold) is harder, holds a polish longer under daily knocks, and costs less. 18ct (75% gold) has a deeper, warmer colour and more gold content, and picks up fine scratches a little faster. Both are proper fine jewellery; the choice is colour and budget, not quality. We compare them properly in 14k vs 18k gold, and the wider decision of carat plus colour is covered in types of gold.

At the bottom of the scale, 9ct is still real solid gold, just the minimum purity Australia sells as gold. It is the hardest and palest of the carats and entirely respectable for everyday pieces.

Both meanings at once, and this is where the confusion peaks. A listing that reads "1 carat diamond ring in 18ct gold" is using the word twice for two different measurements: the diamond weighs 1 carat (0.2 grams), and the band is 18 parts per 24 pure gold. The stone number is a weight. The metal number is a purity.

A related search we see a lot is "1 carat gold", and it is almost always a crossed wire. Gold is not sold at 1 karat (that would be about 4% gold, which no jeweller stamps or sells), so a "1 carat gold ring" in practice means a ring with a 1 carat stone set in gold. If you are sizing up what a 1 carat stone actually weighs and measures on the hand, how much does a carat weigh covers the diamond side of the word properly.

Yes, roughly in proportion to the gold content. An 18ct band contains twice the pure gold of a 9ct band of the same weight, so the metal component of the price roughly doubles. On an engagement ring, though, the metal is usually the smaller share of the cost; the centre stone and the making dominate. Moving from 14k to 18ct typically shifts the ring's price by less than people expect, which is why we suggest choosing carat on colour and wear habits first and price last.

One more thing carat does not do: it does not change how the gold performs as an investment. Jewellery gold of any carat trades on its gold content when melted, and the making, design and stones are not recovered at scrap value. Buy the carat you want to wear.

Carat for gold is purity out of 24 parts: 24ct pure, 18ct at 75%, 14k at 58.3%, 9ct at 37.5%, with the hallmark inside the band spelling it out in parts per thousand. Karat is the same measure in American spelling. Diamond carat is an unrelated unit of weight at 0.2 grams. If a single sentence mentions both, the stone number is weight and the metal number is purity.

Every ring we make is available in 14k or 18ct gold in yellow, white and rose. Browse our engagement rings to see how each carat and colour looks on a real design, made to order in Melbourne.

Thanks for reading,
Jared and Brie