One of the first questions usually asked is: "How many carats is it?" Most believe that carats represent the size of the diamond; however, this is only partially correct. The carat is actually the weight of the diamond. Historically, it represented the weight of a carob seed; thus, the term carat. In more precise measurements, 5 carats is equal to 1 gram. Therefore, two diamonds of the same weight can appear quite different in appearance.
One carat weighs 200 milligrams, or one-fifth (.2) of a gram. This standard has been in use worldwide since 1914, when it was proposed by the International Committee on Weights and Measures. Note that the term "carat" – which is a measurement for precious gems – is different from the term "karat," which refers to gold quality in the United States.
In discussing diamond weight, you often hear the term points used. For example, you might hear that a diamond is 83 points. This has the same meaning as .83 carats, because there are 100 points to a carat. Thus, .50 carats would be the same as 1/2 carat or 50 points, 1.50 carats would be the same as 1 carat and 50 points or one and one half carats.