Diamonds are weighed in carats.
One carat is 0.2 grams.
For practical reasons, carats are broken down in decimals called points. There are 100 points in one carat.
The most common sizes in the jewelry trade range from 0.01 to 3.00 carat. The bigger the stone is, the rarer it is, and more valuable it becomes. However, size often is the least important factor in determining a diamond's ultimate value.