The 4Cs: Carat


Diamond Carat Weight Measures a Diamond’s Apparent Size

Don’t confuse carat with karat, which refers to gold purity (as in 18K gold). Diamonds and other gemstones are weighed in metric carats: one carat is equal to 0.2 grams. Each carat is divided into 100 points. In the diamond industry, weight is rounded to a hundredth of a carat.  Diamond weights higher than one carat are expressed in carats and decimals. Because even a fraction of a carat can make a considerable difference in cost, precision is crucial. Diamond price increases with diamond carat weight because larger diamonds are rarer and more desirable. But two diamonds of equal carat weight can have very different values (and prices) depending on three other factors of the diamond 4Cs: ColorClarity, and Cut.

A 50-point diamond weighs 0.50 carats. A jeweler may describe the weight of a diamond below one carat by its ‘points’ alone, for instance, a 'fifty pointer.’ However, a 1.08 carat stone would be described as ‘one point oh eight carats' or 'one oh eight.' Some weights are considered 'magic sizes': half-carat, three-quarter carat, and carat. Visually, there’s little difference between a 0.99-carat diamond and one that weighs a full carat. But the price differences between the two can be significant. The majority of diamonds used in fine jewelry weigh one carat or less.

How did the carat system start?
The carat, the standard unit of weight for diamonds and other gemstones, takes its name from the carob seed. Because these small seeds had a fairly uniform weight, early gem traders used them as counterweights in their balance scales. The modern metric carat, equal to 0.2 grams, was adopted by the United States in 1913 and other countries soon after. Today, a carat weighs the same in every corner of the world.

This short video explains carat weight and shows how diamonds are weighed in GIA’s lab on an extremely precise electronic scale.