CARAT Refers to the weight of a diamond.
Carat is often confused with size even though it is actually a measure of weight. One carat is equivalent to 200 milligrams. One carat can also be divided into 100 “points.” A .75 carat diamond is the same as a 75-points or 3/4 carat diamond.
A 1-carat diamond costs exactly twice the price of a half-carat diamond, right? Wrong. Since larger diamonds are found less frequently in nature, which places them at the rarest level of the Diamond Quality Pyramid, a 1-carat diamond will cost more than twice a 1/2-carat diamond (assuming color, clarity and cut remain constant).
Cut and mounting can make a diamond appear larger (or smaller) than its actual weight.