Stone Weight Estimator
Estimate a stone's carat weight from millimetre dimensions across seven standard cuts and fifteen gem species, or work backwards from a known weight to expected dimensions. It runs entirely in your browser and nothing is uploaded.
How it works
Pick the cut and species
Choose from seven standard cuts and fifteen common gem species, each carrying its own density and yield figures.
Enter the millimetres
Type the length, width, and depth from a loupe or calliper reading to build the stone's estimated volume.
Read the weight, or reverse it
See the estimated carat weight straight away, or switch to reverse mode to estimate dimensions from a known weight.
Estimation formulas assume average proportions for each cut. Real weight can swing by 10% or more depending on girdle thickness and pavilion depth, so treat this as a fast estimate, not a certificate. Weigh the stone on a scale whenever the number actually matters, such as pricing or insurance.
Want the full accurate-scale workflow guide?
This tool is free to use right now, no email needed. The guide below is optional: it walks through the anchor-measure-verify method behind True-Scale, our other free tool.
Stop shipping AI renders that lie about size. Learn the accurate-scale method.
A practical guide for jewellery brand owners using AI to generate product visuals. Covers the anchor-measure-verify method behind the free True-Scale tool, so every render you publish is true to the piece's real dimensions.
- ·Anchoring a known dimension in any AI-generated image
- ·Verifying feature sizes in true millimetres before you publish
- ·Why AI models render jewellery oversized, and how to catch it
- ·Exporting an annotated spec sheet for casting and quality checks