Find out its weight in grams and divide this by 0.200 (the weight of one carat) to calculate a diamond’s carat weight.
You can also roughly calculate a diamond’s weight based on its cut, diameter, and height in millimeters. But remember that a carat is a unit of weight, it’s not a measure of size. Plus, differences in density mean that two different one-carat diamonds can be of different sizes.
Try Peter Norman’s diamond calculator above if you’d like to get an approximate weight based on millimeters.