CARAT The carat is one of the four most important quality features - the so-called four Cs - that are used to determine the price of diamonds. It is a unit of measurement for the weight of diamonds and other precious stones, where one carat is equal to 0.2 grams. As an alternative to the specification in carats, specification in points is also used for very small diamonds. For this, a carat is divided into 100 points; a half-carat therefore has a weight of 50 points.