The last of the FOUR C's is carat weight (the size of the diamond). In one sense, it is the least important factor in determining a diamond's value. It is important for the owner to know the weight of his diamond, but weight alone is no indication of the comparative values of different diamonds.

A carat is subdivided into 100 points; e.g., a quarter-carat diamond weighs 25 points. All other factors being equal, a 50-point diamond is worth more than two 25-point diamonds of the same quality because larger diamonds are more rare and therefore more valuable.