Diamonds are always measured in carat weight. One carat is the equivalent of 1/5 of a gram. Additionally, there are "100" points in a carat, so that a .50 "point" diamond would be described as a half-carat.

In general, the pricing structure for polished diamonds is directly related to the pricing structure for the diamonds in their rough state. Because there is a scarcity of large diamond rough, the price for these diamonds after polishing will be higher per carat. As you get larger in carat weight there will be an incremental jump in price even between two diamonds of same color and clarity. These plateaus are found approximately every .10-.15 points. Category examples are: .50-.59, .60-.69, .80-.89, .90-.99 carat, etc