A carat is an ancient measure of weight. Originally the seeds from the carob tree were used as weights, because of their almost identical size and weight. The modern interpretation of this is a carat, which by mass is one fifth of a gram or .20 of a gram.

Carats are further divided into points. Each carat has 100 points therefor a half carat diamond or a .50 point stone are the same and are represented by math as .50 CT, which is the abbreviation of carat.