A diamond’s weight is measured in carats.

The carat is subdivided into 100 equal parts called points.
One point equals .01 carat or 1/100 carat. 100 points add up to one carat.

Because round brilliant cuts follow exact standards, you can make a good estimate of the carat weight of the stone based on the stone's diameter. The following chart compares the relative sizes of stones and describes how much a round brilliant diamond of a certain size is likely to weigh. This chart is for educational purposes and represents a guideline for diameter and carat weights. It is not representative of other cuts or shapes. It is also not applicable to colored gemstones which have a different density from diamonds.