Carat Weight Calculator
Estimate the carat weight of a round brilliant diamond from its measured diameter and depth, or convert a known weight between carats, grams and milligrams.
How to estimate carat weight
- To estimate from a stone, enter the girdle diameter and total depth in millimetres.
- To convert a known weight, switch to a unit and enter carats, grams or milligrams.
- Read the carat, gram and milligram values and copy the result.
Examples
Estimate a 6.5 mm round brilliant
diameter 6.5 mm, depth 4.0 mm
about 1.0309 carats (0.2062 g, 206.18 mg)
Convert grams to carats
0.5 grams
2.5 carats
Frequently asked questions
How is carat weight estimated from dimensions?
For a round brilliant the formula is diameter squared times depth times 0.0061, with all measurements in millimetres. It is an estimate, not a substitute for a calibrated scale.
How many grams is one carat?
One metric carat equals exactly 0.2 grams, which is also 200 milligrams. So 5 carats weigh exactly 1 gram.
Does the estimate work for fancy shapes?
The 0.0061 coefficient is tuned for round brilliants. Ovals, princess and other cuts use different coefficients, so the round formula will only give a rough idea for them.
Why does my stone weigh more than the estimate?
A thick girdle, a deep pavilion or a bulging culet all add weight that the basic diameter and depth formula does not capture, so a heavy make can outweigh the estimate.
Is points the same as carats?
Yes. One carat is divided into 100 points, so a 0.25 carat diamond is a 25 point stone and a 0.5 carat stone is 50 points.
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