What is a Karat?

If you operate with gold coins or other gold articles, you will encounter the term Karat (sometimes Carat), which is a measure of purity of gold alloys. One Karat is 1/24 purity by mass, meaning that something (e.g. a gold coin) is only 4.17% gold and 95.83% other metals, and 24 Karat means it's 99.9% fine gold (there's no 100% fine gold yet).

To calculate the fineness using Karat measure, you can just take a Karat measure, divide it by 24, and multiply by 100: 18-karat = 18 / 24 = 0.75, 0.75 * 100 = 75% fine gold. You can see the table on the left for converting karats into fineness.

Karat is not an atomic measure, it is divisible into smaller fractions: 1 Karat = 4 Grains, and 1 Grain = 4 Quarts.

The name "Karat" came from Greek and it was modified version of "fruit of carob", which was apparently a measure of diamonds, and later purity of gold.

Nowadays, Karat is still widely used for making bullion gold coins and jewelleries, but it's getting replaced more often by the millesimal system, which measures the purity of precious metal in parts per thousand, e.g. 999 or 24-karat or 99.9% fine gold.

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