Diamond carat weight, points, and fractions
What a carat is, and how a listing should state weight.
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What a carat is
The Guides say a carat is a standard unit of weight for a diamond, equal to 200 milligrams (1/5 gram). A point is one one-hundredth of a carat.
Points need decimals
Under section 23.18(b), a listing that gives weight in points should also give it in decimal parts of a carat, for example "25 points or .25 carat".
Decimal weights
The FTC says a decimal weight should be accurate to the last decimal place, so ".30 carat" could be a diamond that weighs between .295 and .304 carat. A weight given to one decimal place, such as ".5 carat", should be accurate to the second place, between .495 and .504 carat.
Fractional weights
A fraction may stand for a range. The FTC gives the example that a diamond described as 1/2 carat could weigh between .45 and .54 carat. A seller that uses fractions should say clearly, close to the fraction, that the weight is not exact, and give the range or tolerance it uses.
Total weight
Section 23.18 also covers "total weight". Some listings give one weight for all the stones in a piece. Ask the seller whether a weight is for one stone or for all of them, and which tolerance it uses. That is our tip, not a source's.
Photos and size
A note to section 23.1 says an illustration that shows a diamond or other gemstone larger than its actual size may mislead, unless the listing discloses the true size.
FAQ
General information only. We are not a jeweler, appraiser, or gemological lab, and we do not grade, appraise, or verify any stone or metal. Before you buy, read the seller's full description, including whether a diamond is mined or laboratory-grown, any treatment, the metal's karat or fineness, and the weight, and check any grading report with the lab that issued it.
Next: what is a diamond
The FTC definition, in plain words.
