Carat

Carat is often confused with size even though it is actually a measure of weight. Sometimes, you might think a larger diamond appears more brilliant than a smaller one. This is because light must travel a greater distance through a larger diamond. The result is a prism effect that your eye registers as more brilliance and fire. One carat is divided into 100 "points" so that a diamond of 75 points weights .75 carats.

Size is the most obvious factor in determining the value of a diamond. However, two diamonds of equal size can have very unequal values, depending on their quality. Also, diamonds of high quality can be found in all size ranges. Larger diamonds are found relatively infrequently in nature and therefore more valuable.