Most people think of a carat in relation to the size of the diamond, but it is actually based on weight. The weight of a diamond is traditionally measured in terms of carat, a unit of weight under which 1 carat equals .20 grams. Each carat is divided into 100 points, allowing for a very precise measurement of the diamond. For instance, a diamond that weighs .50 carat may be referred to as a “half-carat” or a “fifty-pointer.”
Two diamonds of equal carat weight can have significantly different costs because of the other factors of cut, color, and clarity. As a diamond increases in size and carat weight, its price will increase accordingly due to larger diamonds being more rare and thus more valuable.