Diamond Carat

Refers solely 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, also known in the trade as a 'three grainer' (a grain being .25ct).

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 colour, clarity and cut remain constant). Cut and mounting can make a diamond appear larger (or smaller) than its actual weight. So shop around and talk to your jeweller to find the right diamond and setting to optimize the beauty of your stone.