The unit of measurement of a diamond is called carat weight or carat in short. 1 carat (ct) is equal to 200 milligrams (mg) in weight wherein each cart is divided into 100 points. Similar to currency, a 0.50 ct. is equal to 50 points and a 0.25 ct. is equal to 25 points. A related term, Total Carat Weight (TCW), this is the total carat weight of several pieces of diamonds. For example, a diamond engagement ring with a center stone of 1.00 ct., side stones of 0.50 ct. and accents stones of 0.32 has a Total Carat Weight of 1.82 TCW
[NOTE: Don't confuse "carat weight" with "karat," the method of determining the purity of gold.]
A diamond's cut grade should also be considered because, as we noted in the cut grade section, when a diamond is cut with the proper proportions, the maximum amount of light (or sparkle) is returned out of the top of the diamond. Thus, when a diamond is well cut, the light reflected out of the top makes it appear larger. In addition, much of the weight of a poorly cut diamond, for example, may be "hidden" in the base of the diamond, making the diamond appear smaller than its carat weight would imply. It is therefore possible to have a diamond of a lower carat weight, but higher cut grade, that appears larger than a diamond with a larger carat weight, but poor cut.