Carat weight calculator
Can’t pull the stone to weigh it? Measure it. Enter the millimetre dimensions and shape, and we’ll estimate carat weight using the same proportion formulas the trade uses.
Round brilliants are symmetrical, so width tracks the diameter automatically.
Estimated weight
1.03
carats
≈ 0.206 g · Round cut
This is an estimate from measurements alone. Cut precision and girdle thickness can shift actual weight by several points.
How the estimate works
Carat weight is proportional to a stone’s volume and the density of diamond. For round brilliants we use diameter² × depth × 0.0061; fancy shapes use length × width × depth × a shape-specific factor. The result is an approximation: real weight varies with girdle thickness, cut precision and exact proportions, so treat it as a guide rather than a grading figure.
Want the exact weight and grade?
Our lab weighs to the hundredth of a carat and certifies the full 4Cs — plus whether your stone is natural, lab-grown or a simulant.
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