Free tool
Diamond carat to mm calculator
The usual size of a stone of a given weight, by shape — or an estimated weight from its measurements. Free, no sign-up.
Carat ↔ millimetres
From weight to size
At a typical 61% depth
Diameter6.45 mm
Depth3.94 mm
From measurements to weight
Estimated weight—
Estimates from the usual formula (length × width × depth × a shape factor). Real stones vary with how they are cut — often by 5–10% — so use the report’s measurements and a scale for anything you buy or sell.
Pricing the stone too? Try the Rap discount calculator, and read why a stone just over a size line is worth so much more in Rapaport discount explained.
Keep every measurement with the stone
Avirat stores length, width, depth, table and the full grading on each stone — searchable, printable on labels. 14 days free.