The Girlfriend's Guide to Jewellery
13: Carat 2011-05-04
Carat describes weight the same way that pound and kilogram do. A carat is a much smaller measure of weight. One carat is equal to 1/5 of a gram. It takes five carats to equal one gram; 5.00cts equal 1 gram. All gemstones are sold by weight, that is, by the carat.
We can think of a carat in the same way as we do a dollar. One dollar is written $ 1.00; one carat is written 1.00ct. A dollar is made up of 100 ‘cents’; a carat is made up of 100 ‘points’. 1/100 of a dollar is one cent, and is written $0.01. 1/100 of a carat is one point, and is written 0.01ct.
We use the word ‘points’ for any size smaller than one carat, that is to say, for weights up to 0.99ct or ninety-nine points. With dollars the single zero before the decimal point is often omitted. With carats it is always included: 0.10ct is ‘ten points’; 0.79ct is ‘seventy-nine points’ and 0.015ct, is ‘one and a half points’.
For a carat or more we say it the way we write it: 1.32ct is ‘one carat thirty-two’ or ‘ one thirty-two’; 17.03ct is said ‘seventeen carats three points’ or ‘seventeen oh three’. For 0.25ct, 0.33ct, 0.50ct and 0.75ct we say ‘a quarter carat, ‘a third of a carat’, ‘half a carat’ and ‘three quarter carat’.