💎 Diamond Weight Calculator
Estimate a diamond’s approximate carat weight from its millimeter measurements, based on its shape.
mm
mm
mm
How Diamond Weight Estimation Works
Jewelers and appraisers commonly estimate a mounted diamond’s carat weight from its visible millimeter measurements when it can’t be weighed directly (for example, while still set in a ring). Each cut shape has its own widely-used estimation factor because the proportions of material differ by shape.
The Formula
Estimated Carat Weight = Length × Width × Depth × Shape Factor, where all measurements are in millimeters. For a round brilliant, length and width are simply the diameter measured twice.
- This is an estimate, not an exact weight — actual weight can vary with the stone’s specific proportions and cut quality.
- For an accurate weight, a loose stone should always be weighed on a certified gem scale.
- 1 carat = 100 points = 0.2 grams.
Last reviewed August 2026