Diamond weight is measured in units called carats. A carat is divided into 100 parts. Each part is called a point. A diamond that weighs one (1.00) carat also weighs 100 points. Small stones like .10, and .15ct are referred by point designations. One carat is equal to 1/5 of a gram (200 milligrams) Diamonds are usually valued in terms of price per carat. Accordingly, for the same color, clarity, and cut, a diamond that weighs more costs more. Also since larger diamonds are also more rare, the cost per carat of equal quality stones also increases as diamond size increases.