Diamond Weight Calculator — Estimate Carats from Dimensions
Use a diamond's physical measurements to estimate its carat weight — no scale needed. Pick the cut, enter the millimetre dimensions, and get an instant Leveridge-formula estimate accurate to within ±5%.
Diamond shape / cut
mm
mm
Industry Leveridge approximation — typically within ±5% of actual weight
- 1
Diameter squared
6.5 × 6.5 = 42.25 - 2
Volume proxy
42.25 × 3.9 = 164.775 - 3
Estimated weight
164.775 × 0.0061 = 1.005Shape factor for Round Brilliant; typically ±5% of true weight.
How does this calculator work?
Estimate diamond weight from caliper measurements: round ct = d² × depth × 0.0061; other cuts use ct = L × W × depth × shape factor (0.0058–0.0092). Results are typically within ±5% of scale weight. Enter dimensions above for an instant estimate across eight popular cuts.
Formula
How this is calculated
Diamond weight is measured in carats (1 ct = 0.2 g). Because most mounted diamonds cannot be weighed directly, gemologists use caliper measurements and standard formulae to estimate weight. The Leveridge formula — named after the tool historically used to measure stones — approximates the diamond as a cylinder or rectangle and then corrects for the actual proportions of each cut using a shape-specific factor.
For a round brilliant the formula is: ct = diameter² × depth × 0.0061, where the 0.0061 constant accounts for the stone being denser than water (diamond SG ≈ 3.52), the metric carat (0.2 g), and the fact that the brilliant cut fills roughly 61% of an enclosing cylinder. For non-round cuts, the formula becomes ct = length × width × depth × factor; the factor differs per shape because princess cuts are more "full" while pear and marquise cuts have points that remove material.
This approach is an estimate — the real weight also depends on girdle thickness, facet symmetry and cutting style. Expect accuracy within about ±5% for well-proportioned commercial-grade stones. For insurance, grading reports, or legal purposes, always use a precision balance on the loose stone.
Frequently asked questions
For typical commercial diamonds with standard proportions the formula is usually within ±5% of the true weight. Very deep or very shallow cuts, unusual girdle thickness, or fancy modified cuts may push the error higher. For insurance or sale purposes, weigh the loose stone on a precision balance.
Yes — that is the primary use case. Measure the diameter (or length/width) across the girdle with digital calipers and estimate the depth from the setting height minus the bezel thickness. The estimate will be slightly less precise than for a loose stone, but usually sufficient for everyday purposes.
A carat (ct) is a unit of mass equal to 0.2 grams, used for gemstones. A karat (k or kt) is a measure of gold purity (24k = pure gold). They sound similar but measure completely different things.
Also known as
TG we-Calculate Editorial Team. (2026). Diamond Weight Calculator — Estimate Carats from Dimensions [Online calculator]. TG we-Calculate. https://we-calculate.com/calculator/diamond-weight-calculator
TG we-Calculate Editorial Team. "Diamond Weight Calculator — Estimate Carats from Dimensions." TG we-Calculate. 2026. https://we-calculate.com/calculator/diamond-weight-calculator.
TG we-Calculate Editorial Team, "Diamond Weight Calculator — Estimate Carats from Dimensions," TG we-Calculate, 2026. [Online]. Available: https://we-calculate.com/calculator/diamond-weight-calculator
@misc{wecalculate_diamond_weight_calculator, title = {Diamond Weight Calculator — Estimate Carats from Dimensions}, author = {{TG we-Calculate Editorial Team}}, howpublished = {\url{https://we-calculate.com/calculator/diamond-weight-calculator}}, year = {2026}, note = {TG we-Calculate} }
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