Carat - A carat is the universal measure of weight for a diamond. It's the easiest of the 4C's to determine, but two diamonds of equal size can have very different values because the quality is still determined by the color, clarity, and cut. A carat is 0.2 grams and there are 100 points (or 200 milligrams) per carat. Larger diamonds are found relatively infrequently in nature, which puts them at the rarest level of the Diamond Quality Pyramid.