Carat

Diamonds are sold by the carat. Carat refers to a unit of weight, not size. One carat equals 1/5 of a gram, or 200 milligrams. A one-carat diamond can look larger or smaller depending on its individual proportions (see "Cut") and still weigh 1.00 carat. Diamonds of the finest quality are sold for the highest prices per carat and progressively lower quality diamonds are sold for lower prices per carat. Also, there are price increases at every 1/4-carat mark due to an increase in the diamond's rarity.

The approximate sizes of round diamonds are shown below. The larger the diamond, the more rare it is, and the more it costs. Because of these 1/4-carat increases, purchasing a diamond that weighs .96 carat instead of 1.00 carat may save you hundreds of dollars while the size difference will be negligible.

When discussing diamonds, jewelers might use an expression such as "this diamond weighs 57 points." The term point also refers to weight. A point is equal to 100th of a carat; therefore a 1-carat diamond is equal to 100 points. Just as there are 100 pennies to a dollar there are 100 points to a carat.