Diamond weight is measured in carats, a small unit of measurement equal to 200 milligrams. Each carat is divided into 100 points. Therefore, a half-carat stone may be referred to as a “50-pointer” or “50-points”. Carat weight is the easiest of the 4 C’s for gemologists to determine due to the use of highly sophisticated measuring equipment.
Two diamonds of equal carat weight might vary greatly in value depending upon their cut, color and clarity. This is important because when mounted, one diamond may appear larger than the other, although they actually weigh the same. If size is important to you, focus on diamond measurements as opposed to carat weight. Diamonds that look big for their weight may have reduced brilliance and fire so always insist on great cut.
An increase in carat weight does not produce the same increase in millimeter diameter. For example, there is a 25% increase in carat weight from 1.00 carats to 1.25 carats but less than 8% increase in diameter (6.5 to 7.0 mm). This concept, along with the increased price per carat, explains why prices increase dramatically in order to get noticeably bigger millimeter size.