Carat is a measurement of a diamond’s weight and size, not to be confused with “karat”, which is used to determine the purity of gold.  The term carat originates from the Greek term keratin for “fruit of the carob”.  Carob seeds were used for precision weighing of gold and gemstones, since it was thought that carob seeds had a uniform weight.  The modern carat, known as the metric carat, was adopted in 1907, and is a simple measurement of weight used for the evaluation of all gemstones.  

The weight of any gemstone is measured in carats (ct); one carat is equal to 0.20 grams. Carat weight alone does not define a diamond’s value. Two diamonds of equal weight can vary widely in price because of quality differences. When considering diamonds of equal quality, the larger ones will have more value. Although larger stones are often thought to be more expensive and desirable it is important to remember that a diamond’s value is determined using all the 4Cs, not just their carat weight.