Moissanite vs diamond size: same carat, different mm
By HeyGema™ · Updated
In short
A round 1 carat moissanite measures 6.6 mm and a round 1 carat diamond 6.5 mm, so the moissanite is 3% wider. Moissanite is usually sold by diamond equivalent weight, which matches the diamond size.
- 6.6 mm1 ct moissanite
- 6.5 mm1 ct diamond
- +3%width vs diamond
Carat to mm calculator
About 6.6 x 6.6 mm
An estimate for a well-cut stone. A deep or shallow cut faces up smaller or bigger.
Moissanite vs diamond size at the same carat weight
Moissanite is lighter than diamond (density 3.22 against 3.52), so a 1 carat moissanite is slightly larger than a 1 carat diamond: 6.6 mm against 6.5 mm. Shops often label moissanite by diamond equivalent weight (DEW), which is the weight of a diamond of the same size. That is why a stone sold as "1 carat" is usually about 0.91 carat on the scale.
- 0.5 ct
- Diamond (round): 5.1 mm
- Moissanite (round): 5.3 mm
- Difference in width: +3%
- 1 ct
- Diamond (round): 6.5 mm
- Moissanite (round): 6.6 mm
- Difference in width: +3%
- 1.5 ct
- Diamond (round): 7.4 mm
- Moissanite (round): 7.6 mm
- Difference in width: +3%
- 2 ct
- Diamond (round): 8.1 mm
- Moissanite (round): 8.4 mm
- Difference in width: +3%
- 3 ct
- Diamond (round): 9.3 mm
- Moissanite (round): 9.6 mm
- Difference in width: +3%
- 4 ct
- Diamond (round): 10.2 mm
- Moissanite (round): 10.5 mm
- Difference in width: +3%
- 5 ct
- Diamond (round): 11.0 mm
- Moissanite (round): 11.4 mm
- Difference in width: +3%
Moissanite vs diamond at the same size in mm
If you shop by millimeters, the weight changes instead. A round moissanite of a given size weighs less than a diamond of that size.
- 4 mm
- Diamond weight: 0.24 ct
- Moissanite weight: 0.22 ct
- 5 mm
- Diamond weight: 0.47 ct
- Moissanite weight: 0.43 ct
- 6 mm
- Diamond weight: 0.8 ct
- Moissanite weight: 0.74 ct
- 6.5 mm
- Diamond weight: 1.02 ct
- Moissanite weight: 0.94 ct
- 7 mm
- Diamond weight: 1.28 ct
- Moissanite weight: 1.17 ct
- 8 mm
- Diamond weight: 1.91 ct
- Moissanite weight: 1.75 ct
- 9 mm
- Diamond weight: 2.72 ct
- Moissanite weight: 2.49 ct
- 10 mm
- Diamond weight: 3.73 ct
- Moissanite weight: 3.41 ct
What diamond equivalent weight means
A moissanite listed as 1 carat DEW has the face-up size of a 1 carat diamond (6.5 mm). Its true weight is about 0.91 carat. Check whether a listing gives the real weight or the diamond equivalent, and compare millimeters. The moissanite size chart shows every round and fancy size by DEW.
Moissanite facts that affect size
Specific gravity 3.20 to 3.22, hardness 9.25 on the Mohs scale and refractive index 2.65 to 2.69. Almost always lab created. Sold by size in mm, labeled with a diamond equivalent weight.
How much the cut changes this
These sizes assume a well-cut stone of typical depth. A deep cut hides weight in the lower part of the stone and measures smaller across; a shallow cut spreads it and measures larger. Treat the figures as a guide within a few percent. See the methodology.