The metric carat is a legal unit of measurement for the mass or weight of precious stones. It is defined in DIN standard 1301-1. One metric carat corresponds to 0.2 g or 200 mg. It is also probably the best-known term when it comes to grading diamonds. However, the weight should not be confused with the size. Two diamonds can both weigh one carat, but be different sizes.
Etymologically, the term is derived from the ancient Greek keration, meaning “horn-shaped”. This described the fruit pod of the carob tree, the seeds of which were often used as weights in the past thanks to their uniform size. In the Middle Ages, one carat corresponded to the weight of three barley or four wheat grains.
In order to achieve worldwide uniformity, the metric carat (carat métrique), with its current value, was defined in 1907. Since then, diamonds have been measured in carats. Please note that the unit of measurement carat (abbreviated to ct) should not be confused with the unit carat (ct) which is used to describe the fineness of gold in a piece of jewellery and can also be spelled karat (abbreviated to k).
The other three Cs being equal, it is the carat measurement which determines the value of a diamond, increasing exponentially. This is because large diamonds are significantly rarer than small diamonds.
Important to know
The four Cs make it possible to compare and judge diamonds objectively. However, numbers alone are often inadequate when it comes to describing the mysterious and captivating beauty of a diamond, for that you should visit your jeweller and see the stones with your own eyes.
Only a specialist can make price comparisons beyond the four C criteria, especially for stones with the same certificate designation. In addition to the four Cs, experts can evaluate diamonds by considering their fluorescence, condition, expression and colour.
Round cut (brilliant cut)