“Carats,” are commonly referenced when referring to the size of a diamond but carats are actually a specification of weight. As a result different shapes and cuts of diamonds can appear larger than others that possess slightly higher carat-weights.

The word carat originated from the Greek word for carob tree or Ceratonia siliqua. The tiny seeds of this tree are known for their uniformity and consistent weight.

Beginning in the late 16th century diamonds and gemstones were weighed on a mercantile scale against these seeds. However, merchants often used two sets of carob seeds, one lighter and one heavier, in order to trick prospective buyers and sellers. As a result of these discrepancies the system was standardized in the early 20th century when a single carat was fixed at 0.2 or one fifth of a gram.


Just as a dollar is divided into 100 pennies, a carat is divided into 100 points. For example, a 50-point diamond weighs 0.50 carats. But two diamonds of equal weight can have very different values depending on the other members of the Four C’s: clarity, color and cut. The majority of diamonds used in fine jewelry weigh one carat or less.

Because even a fraction of a carat can make a considerable difference in cost, precision is crucial. In the diamond industry, weight is often measured to the hundred thousandths of a carat, and rounded to a hundredth of a carat. Diamond weights greater than one carat are expressed in carats and decimals. (For instance, a 1.08 ct. stone would be described as “one point oh eight carats,” or “one oh eight.”)