Carat weight

A carat is based on the original scale used to measure Diamonds weight, that being the carob nut. Now however it is measured more accurately, each carat being the equivalent of one fifth of a gram (0.2grms).
Each carat is divided into 100 points, for example half a carat (0.50cts) will be 50 points, a quarter carat 25 points (0.25cts) and so on. A full cut brilliant Diamond can be as small as half a point (0.005cts). The carat weight of a stone plays a big factor on price, especially once the stone is larger than a carat. This is because less than 5% of gem quality diamonds found are over one carat in size, so good quality stones in this size and greater are comparatively rare.
This is an accurate and definitive statistic which is found on a Diamond certificate, due to its weight being relatively simple to measure and check using scales.