The weight of a diamond is expressed in carats. 1 carat equals 0.2 grams. A carat is further subdivided into 100 points.
0.50 ct = 1/2 carat = 50 points.
Weight is the most obvious factor in determining the value of a diamond. But two diamonds of equal weight can have very unequal values, depending on their quality. Furthermore weight only indicates size. Depending on proportions two diamonds weighing the same may appear very different in size. Internationally, the weight of a diamond is mentioned to two decimal places.