Carat weight is the weight of a gemstone. One carat is 200 milligrams, a fifth of a gram, and it has 100 points.
In more detail
Carat is weight, not size. Width grows only with the cube root of weight. So a 2 ct diamond is only about 26% wider than a 1 ct. In our simulator, a 1.00 ct T73 diamond is 6.48 mm across and a 2.00 ct is 8.16 mm.
On a grading report
In the grades block, to the hundredth of a carat. GIA's balance reads to five decimal places and IGI's to four; both report two.
Related terms
- Magic sizes: Magic sizes are round-number weights, such as half a carat or one carat. They sell for more because of demand, not looks.
- Measurements: Measurements is the report line that gives a stone's size in millimeters. A round reads minimum – maximum diameter × depth, and a fancy shape length × width × depth.
- Four Cs: The four Cs are color, clarity, cut and carat weight: four scales that describe the quality of a diamond. GIA made them into a grading system in the 1950s.
- Weight ratio: Weight ratio is the part of GIA's cut grade that compares a diamond's weight with its diameter. A stone can carry too much or too little weight for its width.
- Specific gravity: Specific gravity compares a stone's weight with the weight of the same volume of water. It decides how much a stone of a given size weighs.