Carat Weight

Diamond carat weight is the measurement of how much a diamond weighs and thus reflecting its apparent size. The carat, the standard unit of weight for diamonds, 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.

Today diamonds and other gemstones are weighed in metric carats: one carat is equal to 0.2 grams or 200 milligrams, about the same weight as a paperclip. (Don’t confuse carat with karat, as in “18K gold,” which refers to gold purity.)

Because even a fraction of a carat can make a considerable difference in cost, precision is crucial. Therefore, just as a dollar is divided into 100 pennies, a carat is divided into 100 points. For example, a 50-point diamond weighs 0.50 carats and may be described in the diamond industry as a “50 pointer”. Diamond weights greater than one carat are expressed in carats and decimals. For example, a 1.08 carat diamond would be described as “one point oh eight carats,” or “one oh eight.”


Some weights are considered “magic sizes”. These are 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.

Also consider that two diamonds of equal weight can have very different values depending on the other members of the Four C’s: clarity, colour and cut. It follows then that all else being equal, diamond price increases with diamond carat weight because larger diamonds are rarer and more desirable. The majority of diamonds used in fine jewellery weigh one carat or less.

Diamond Carat Weight Grading by GIA

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

Diamond 4Cs