- a unit of weight in gemstones, 200 milligrams (about 3 grains of troy or avoirdupois weight). Abbreviation: c., ct.
- karat.
- a measure of the weight of precious stones, esp diamonds. It was formerly defined as 3.17 grains, but the international carat is now standardized as 0.20 grams
- a measure of the proportion of gold in an alloy, expressed as the number of parts of gold in 24 parts of the alloy
