Reference Guide
Moissanite Size & Weight Guide vs Diamond
Same millimeter dimensions, different carat weight. Use this interactive guide to find the exact diamond-equivalent size for every moissanite shape — round, oval, cushion, princess, emerald, pear, marquise, radiant, heart, and asscher.
Moissanite specific gravity: 3.21 · Diamond: 3.52
Same mm size = moissanite weighs ~9% less in carats
Face-up appearance is visually identical when set
| Size (mm) | Moissanite (ct) | Diamond equiv. (ct) | Weight diff. | Notes |
|---|
3.21
Moissanite specific gravity
Moissanite has a specific gravity of 3.21, compared to diamond's 3.52. This is why a moissanite stone with the exact same millimeter dimensions as a diamond will always weigh approximately 9–10% less in carats.
2.65
Higher refractive index
Moissanite's refractive index is 2.65–2.69, surpassing diamond's 2.42. This means moissanite bends light more, producing exceptional brilliance and fire — especially visible in round and radiant cuts.
9.25
Hardness on Mohs scale
At 9.25–9.5 on the Mohs scale, moissanite is the second hardest gemstone in the world after diamond (10). Highly suitable for daily-wear jewelry including engagement rings.
~9%
The weight difference
For the same mm size, moissanite weighs roughly 9% less than diamond. A 6.5mm moissanite — the classic "1 ct diamond look" — actually registers about 0.95 ct on a gem scale.
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