Cubic zirconia vs diamond size: same carat, different mm
By HeyGema™ · Updated
In short
A round 1 carat cubic zirconia measures 5.5 mm and a round 1 carat diamond 6.5 mm, so the cubic zirconia is 15% narrower. That comes from density: cubic zirconia is 5.80 and diamond is 3.52.
- 5.5 mm1 ct cubic zirconia
- 6.5 mm1 ct diamond
- -15%width vs diamond
Carat to mm calculator
About 5.5 x 5.5 mm
An estimate for a well-cut stone. A deep or shallow cut faces up smaller or bigger.
Cubic zirconia vs diamond size at the same carat weight
Cubic zirconia is much denser than diamond (about 5.8 against 3.52), so a 1 carat stone is far smaller: 5.5 mm against 6.5 mm. To match the size of a 1 carat diamond you need a cubic zirconia of about 1.65 carat.
- 0.5 ct
- Diamond (round): 5.1 mm
- Cubic zirconia (round): 4.3 mm
- Difference in width: -15%
- 1 ct
- Diamond (round): 6.5 mm
- Cubic zirconia (round): 5.5 mm
- Difference in width: -15%
- 1.5 ct
- Diamond (round): 7.4 mm
- Cubic zirconia (round): 6.3 mm
- Difference in width: -15%
- 2 ct
- Diamond (round): 8.1 mm
- Cubic zirconia (round): 6.9 mm
- Difference in width: -15%
- 3 ct
- Diamond (round): 9.3 mm
- Cubic zirconia (round): 7.9 mm
- Difference in width: -15%
- 4 ct
- Diamond (round): 10.2 mm
- Cubic zirconia (round): 8.7 mm
- Difference in width: -15%
- 5 ct
- Diamond (round): 11.0 mm
- Cubic zirconia (round): 9.3 mm
- Difference in width: -15%
Cubic zirconia vs diamond at the same size in mm
If you shop by millimeters, the weight changes instead. A round cubic zirconia of a given size weighs more than a diamond of that size.
- 4 mm
- Diamond weight: 0.24 ct
- Cubic zirconia weight: 0.39 ct
- 5 mm
- Diamond weight: 0.47 ct
- Cubic zirconia weight: 0.77 ct
- 6 mm
- Diamond weight: 0.8 ct
- Cubic zirconia weight: 1.33 ct
- 6.5 mm
- Diamond weight: 1.02 ct
- Cubic zirconia weight: 1.69 ct
- 7 mm
- Diamond weight: 1.28 ct
- Cubic zirconia weight: 2.11 ct
- 8 mm
- Diamond weight: 1.91 ct
- Cubic zirconia weight: 3.14 ct
- 9 mm
- Diamond weight: 2.72 ct
- Cubic zirconia weight: 4.48 ct
- 10 mm
- Diamond weight: 3.73 ct
- Cubic zirconia weight: 6.14 ct
Cubic zirconia facts that affect size
Specific gravity 5.6 to 6.0, hardness 8 to 8.5 on the Mohs scale and refractive index 2.15 to 2.18. Much denser than diamond, so a stone of the same weight is much smaller. It is sold by size in mm.
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.