Work out gold purity converter (karat) instantly with clear inputs, formula shown and shareable results.
Karat expresses gold content in twenty-fourths, so 18 kt is 18/24 or 75% gold - hallmarked as 750 fineness. A 10 g 18 kt ring holds 7.5 g of gold and 2.5 g of alloying copper and silver. Pure 24 kt gold is too soft for most jewellery, which is why alloys dominate.
Purity
fraction = karat / 24
Fineness
fineness = purity x 1000, the hallmark figure
24 kt (999), 22 kt (916), 18 kt (750), 14 kt (585) and 9 kt (375). Hallmarking law sets the permitted marks in each country.
Purer, not better. Higher karat is softer and scratches more easily, so 18 kt is often the practical optimum for worn jewellery.