Carat

The carat is the unit of weight of a diamond. Carat is often confused with size even though it is actually a measure of weight. One carat equals 200 milligrams or 0.2 grams. Often diamond weight is declared in points. One carat is equal to 100 points. Thus, a .75 carat diamond is equivalent to 75 points. The word comes from the carob bean, whose consistent weight was used in times past to measure gemstones.

Once cut, color, and clarity grade have been determined, the carat weight of a diamond can easily be established to fit within a budget. When diamonds are mined, large gems are discovered much less frequently than small ones, which make large diamonds much more valuable. In fact, diamond prices rise exponentially with carat weight. For example, a 2-carat diamond of a given quality is always worth more than two 1-carat diamonds of the same quality. A diamond of double the weight costs around four times more. The cutoff weights are 1/2ct, 3/4ct, 90 points, 1ct, 1.5ct, and 2ct. 'Under-sizes' are diamonds that weigh just below a cutoff weight and while fewer exist, they represent an exceptional value.

Total carat weight (t.c.w.) is a phrase used to describe the total mass of diamonds or other gemstone in a piece of jewelry when more than one gemstone is used. Diamond solitaire earrings, for example, are usually quoted in t.c.w., indicating the mass of the diamonds in both earrings and not each individual diamond.