Diamond & Gemstone Carat Calculator
Estimate carat weight from measurements. Enter your stone's dimensions in millimeters to get an approximate carat weight using industry-standard formulas.
Formula for Round:
diameter² × depth × 0.0061
Important Notes
- • These are estimates only. Actual carat weight can vary based on cut proportions, symmetry, and girdle thickness.
- • For diamonds, these formulas assume standard proportions. Fancy cuts or unusual depths will affect accuracy.
- • Different gemstones have different specific gravities—these formulas are calibrated for diamonds. Colored stones may vary ±10-15%.
- • For accurate weight, always use a calibrated gemological scale.
Understanding Carat Weight Estimation
Carat weight is one of the 4Cs that determines a diamond's value. When a stone is already set, jewelers use measurement-based formulas to estimate the carat weight without removing the stone from its mounting.
How These Formulas Work
Each shape has a different multiplier based on its typical proportions. Round brilliants, with their symmetrical shape, use diameter² × depth. Fancy shapes use length × width × depth, with multipliers adjusted for how much of the measured "box" each shape actually fills.
Why Estimates Vary
A shallow stone of the same diameter weighs less than a deep one. A stone with a very thick girdle adds weight that isn't visible face-up. These formulas assume "average" proportions—actual weights may be 5-10% different depending on the stone's specific cut characteristics.
When Precision Matters
For insurance appraisals, estate valuations, or significant purchases, always have the stone weighed on a calibrated scale. These estimates are useful for quick assessments, but they're no substitute for actual measurement.
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