Diamonds are measured in carats, a small unit of measurement equal to 200 milligrams. A gem stone's carat weight should not be confused with the "karat" weight of gold, which is actually a measurement of purity rather than weight. Each carat is divided into 100 points. Therefore, a half-carat stone may be referred to as a "50-pointer," a quarter carat, "25-points," etc. Carat is the easiest of the 4 C's to determine because of the use of sophisticated measuring equipment. However, two diamonds of equal carat weight might vary greatly in value depending upon their cut, color and clarity. This is important because when mounted, one diamond may appear larger than another, although they actually weigh the same.