What does carat mean in jewellery?
By Jared James · Last updated 21 May 2026
Definition
Carat has two separate meanings in jewellery and it is worth knowing which is which. For gemstones, a carat is a unit of weight equal to 200 milligrams, or one fifth of a gram, so a 1-carat diamond weighs exactly 0.2g. For gold, carat (also written ct or, in American usage, karat) measures purity as parts per 24, so 18ct gold is 18 parts pure gold and 6 parts alloy. In Australia and the UK the minimum legal standard for gold sold as gold jewellery is 9ct.
Frequently asked questions
- Is carat the same as karat?
- They mean the same thing for gold, where carat and karat are simply different spellings of the same purity scale, with karat being the American usage. For gemstone weight, only carat is used, never karat.
- Does a higher carat diamond look bigger?
- A higher carat weight means the stone is heavier, and a heavier stone is usually physically larger too, though shape affects how big a stone looks face-up. A well-cut 1-carat round brilliant will look noticeably larger than a poorly cut stone of the same weight.
- What is a carat of gold in Australia?
- In Australia, gold carat tells you the purity of the alloy. The minimum standard sold as gold jewellery is 9ct, which is 37.5% pure gold, and pieces go up through 14ct, 18ct, 22ct and 24ct. Most fine jewellery in Australia is made in 9ct or 18ct gold.
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