A diamond’s weight is measured in carats. For two diamonds carrying the exact cut, colour and clarity, the value goes up with the weight. One carat is equal to 0.2 gram, and is divided into 100 points.
As shown, a diamond of 25 points would be labeled as 0.25 carat, and so on.

Two diamonds of equal carat weight could be of very different values depending on their cut, colour and clarity.