Carat (mass)

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For other uses of the word carat, see Carat.

The carat is a unit of mass used for gems, and equals 200 milligrams or 3.086 grains (avoirdupois). The word derives from the Greek keration (fruit of the carob), via Arabic and Italian. Carob seeds were used as weights on precision scales because of their reputation for having a uniform weight; a 2006 study <ref>Seed size variability: from carob to carats</ref> by Lindsay Turnbull & others found this to not be the case - carob seeds have as much variation in their weights as other seeds.<ref name=carob>New Scientist, pg 20, 6 May 2006</ref> In the distant past, different countries each had their own carat, roughly equivalent to a carob seed.

Eventually, it was linked to the grain in the Troy pound system of measurement. Under this system the standard was about 205 milligrams. Metric countries used this measurement nonetheless in its limited range of application. In 1907 the metric carat of 200 milligrams was adopted, and is now universally used today. A carat can also be further divided into 100 "points" of 2 milligrams each.

For diamonds, a paragon is a diamond weighing 100 carats (20 grams).

The ANSI X.12 EDI standard abbreviation for carat is 'CD'.