Carat (mass)

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The carat is a unit of mass equal to 200 mg (0.007055 oz), and it is used for measuring gemstones and pearls.

The current definition, sometimes known as the metric carat, was adopted in 1907 at the Fourth General Conference on Weights and Measures, and soon afterwards in many countries around the world.[1] The carat is divisible into one hundred points of two milligrams each. Other subdivisions, and slightly different mass values, have been used in the past in different locations.

In terms of diamonds, a paragon is a flawless stone of at least 100 carats (20 g).

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



First attested in English in the middle 15th century, the word carat came to English from Middle French carat, in turn from Italian carato, which came from Arabic qīrāṭ (قيراط), a term for a very small unit of weight defined by reference to a small seed, which in turn comes from Greek κεράτιον (kerátion), literally meaning "small horn"[2] (diminutive of κέρας - keras, "horn"[3]) but also "carob seed"[4] which was used as a unit of weight.[5] The Latin word for carat is siliqua. In past centuries, different countries each had their own carat unit, all roughly equivalent to the mass of a carob seed, though the carob seed itself was not used as the standard reference point for the weight. These units were often used for weighing gold.

Historical definitions in the United Kingdom

Board of Trade carat

In the United Kingdom, before 1888, the Board of Trade carat was exactly 3\,\tfrac{1647}{9691} (≈ 3.170) grains;[6] after 1887, the Board of Trade carat was exactly 3\,\tfrac{17}{101} (≈ 3.168) grains.[7] Despite it being a non-metric unit, a number of metric countries used this unit for its limited range of application.

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