SAPPHIRE BANKTOOLS
Sapphire Calculator
Estimate carat weight from millimetre dimensions, or convert a total price into price per carat — the unit the gemstone trade actually prices in.
Estimated weight
1.73 ct
Plausible range 1.56–1.90 ct depending on cut depth
An estimate for cut corundum using standard shape factors and a specific gravity of 4.00. Checked against 10 stones in our own inventory that have both measured dimensions and certified weight: median error 2.2%, 9 of 10 within 10%. Deep or shallow cutting shifts the result, so treat this as a guide, never a substitute for a scale or a lab report.
Frequently asked
How do you estimate sapphire carat weight from mm?
Multiply length x width x depth in millimetres by a specific gravity of 4.00, then by the shape factor for the cut (roughly 0.0020 for oval, 0.0022 for cushion, 0.0025 for emerald cut). This is the standard trade estimation for cut corundum. We checked it against 10 stones in our own inventory that have both measured dimensions and certified weight: median error 2.2%.
Is mm to carat conversion accurate?
It is reliable as a guide for normally proportioned stones. A deeply cut stone weighs more than the estimate and a shallow stone weighs less. No estimate replaces a scale or a laboratory report.
Why does price per carat matter more than total price?
The trade prices coloured stones per carat while listings usually quote a total, so converting is the only way to compare two stones of different sizes honestly. Note that per-carat rises sharply with size: a 5 carat stone of equal quality costs far more per carat than a 1 carat.
Browse the collection
Every stone lists price per carat, origin and treatment status, with GRS or GIA certification on request and a 12-month buyback guarantee.