Carat refers to the weight of a diamond. Often mistaken with size, carat is actually a measure of weight. The term carat is a derivative of the word carob. Carob seeds, which are surprisingly uniform in weight, were used as a reference for diamond weight in ancient civilisations. One carob seed equalled one carat. 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-point or 3/4 carat diamond.