Although commonly thought to refer to the size of a diamond, a Carat is a standard unit of measure that defines the weight of a diamond.
Larger diamonds are found much less frequently in nature. Thus, for example, a 1 Carat diamond will cost more than twice that of a 0.50 Carat diamond (assuming Colour, Clarity and Cut remain constant).
The size of a finished polished diamond is directly related to its Carat weight. However, the actual dimensions are entirely dependent upon its proportions. On average, a well proportioned 1 Carat round brilliant cut diamond has a diameter of approximately 6.4mm. In comparison, a shallow cut diamond of the same weight may be anything up to 20% larger in diameter, whereas a deep cut diamond of the same weight may be as much as 20% smaller in diameter. Neither of these variations will sparkle as much as a well proportioned diamond.
The word Carat is derived from the ancient words “Keration” (Greek) and “Qirrat” (Arabic), both of which were names given to the seeds of the Locust or Carob Tree. Due to their relatively consistent size and weight, dried Carob seeds were once widely used by merchants as counterweights for weighing gold, diamonds, gemstones and pearls.
In 1913, after many attempts to standardise the weight of the Carat, the United States, United Kingdom and Europe adopted the use of the Metric Carat, which has become the standard unit of weight used throughout the diamond and gemstone industry today: 1 Carat = 0.2 Grams.
A Carat is further divided into Points, a unit of weight used only for diamonds: 1 Point = 0.01 Carat.