Carat (ct)
A unit of weight for gemstones: one carat is 200 milligrams, divided into 100 points.
Easily confused with
How to read it
GIA defines the metric carat as 200 milligrams, subdivided into 100 points, and notes that carat measures weight, not size. The FTC’s jewelry guides use the same definition: a carat is 200 milligrams, and a point is one hundredth of a carat. GIA traces the word to carob seeds, which early traders used as counterweights.
Also searched as: carat weight, ct, diamond carat, points.
Grades describe a stone as a grading laboratory saw it. This page explains the grading scales; it doesn’t grade or value any stone.
Carat or karat?
Two different measures. For gemstones, carat is weight; for gold, the fineness is counted in karats, as in 14K. The UK’s Hallmarking Act spells both carat and draws the same line: for a precious stone, carat is used as a measure of weight, not of fineness.
Read next
- Next in Diamond gradingCushion cutA square or rectangular diamond with rounded corners, like a pillow.
- The same shape in US state flagsFlag of PennsylvaniaPennsylvania’s flag is the Commonwealth’s coat of arms on a blue field: two black horses either side of a shield with a ship, a plough and three sheaves of wheat, an eagle above, and the motto “Virtue, Liberty and Independence”. The Pennsylvania Senate says the ship stands for the state’s commerce, the plough for its natural resources and the sheaves for its harvests and its wealth in human thought and action.
More diamond grading
The same shape elsewhere
Browse symbols drawn with letters and numbers or squares and rectangles.
Sources
- Diamond Carat Weight (GIA 4Cs), Gemological Institute of America
- Guides for the Jewelry, Precious Metals, and Pewter Industries (16 CFR Part 23), 16 CFR Part 23 (1 January 2021 edition), Federal Trade Commission, published by the U.S. Government Publishing Office, § 23.18, note
- Hallmarking Act 1973, Schedule 1, Hallmarking Act 1973 (c. 43), Sch. 1, Pt. III, legislation.gov.uk (The National Archives), Sch. 1, Pt. III
Researched, edited and approved by Rory Hansen before publishing. Last reviewed September 27, 2026. How we research
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