Topaz size chart: carat to mm for every shape
By HeyGema™ · Updated
In short
A 1 carat round topaz measures about 6.4 mm across, against 6.5 mm for a 1 carat diamond. Topaz has about the same density as diamond (3.53 against 3.52), so the same weight gives the same size.
- 6.4 mm1 carat round topaz
- 3.53density, g/cm3
- 8hardness, Mohs
Carat to mm calculator
About 6.4 x 6.4 mm
An estimate for a well-cut stone. A deep or shallow cut faces up smaller or bigger.
Topaz size chart: carat to mm
Face-up length and width in mm of a well-cut topaz at each weight and shape. Topaz has about the same density as diamond (3.53 against 3.52), so the same weight gives the same size.
| Weight | Round | Oval | Cushion | Emerald cut | Pear | Princess |
|---|---|---|---|---|---|---|
| 0.25 ct | 4.1 | 5.0 x 3.5 | 3.5 x 3.5 | 4.4 x 3.1 | 5.3 x 3.5 | 3.5 x 3.5 |
| 0.5 ct | 5.1 | 6.3 x 4.4 | 4.4 x 4.4 | 5.6 x 4.0 | 6.7 x 4.4 | 4.4 x 4.4 |
| 0.75 ct | 5.9 | 7.3 x 5.0 | 5.1 x 5.1 | 6.4 x 4.5 | 7.7 x 5.0 | 5.0 x 5.0 |
| 1 ct | 6.4 | 8.0 x 5.5 | 5.6 x 5.6 | 7.0 x 5.0 | 8.5 x 5.5 | 5.5 x 5.5 |
| 1.5 ct | 7.4 | 9.1 x 6.3 | 6.4 x 6.4 | 8.0 x 5.7 | 9.7 x 6.3 | 6.3 x 6.3 |
| 2 ct | 8.1 | 10.1 x 6.9 | 7.0 x 7.0 | 8.8 x 6.3 | 10.7 x 6.9 | 6.9 x 6.9 |
| 3 ct | 9.3 | 11.5 x 7.9 | 8.1 x 8.1 | 10.1 x 7.2 | 12.2 x 7.9 | 7.9 x 7.9 |
| 4 ct | 10.2 | 12.7 x 8.7 | 8.9 x 8.9 | 11.1 x 7.9 | 13.5 x 8.7 | 8.7 x 8.7 |
| 5 ct | 11.0 | 13.7 x 9.4 | 9.6 x 9.6 | 12.0 x 8.5 | 14.5 x 9.4 | 9.4 x 9.4 |
| 10 ct | 13.9 | 17.2 x 11.8 | 12.1 x 12.1 | 15.1 x 10.8 | 18.3 x 11.8 | 11.8 x 11.8 |
Length x width in mm. A round stone shows one number, its diameter.
mm to carat for a round topaz
If you know the size, this is the weight. Measure across the widest point of the stone, face up.
- 4 mm
- Weight: 0.24 ct
- 5 mm
- Weight: 0.47 ct
- 6 mm
- Weight: 0.81 ct
- 7 mm
- Weight: 1.28 ct
- 8 mm
- Weight: 1.91 ct
- 9 mm
- Weight: 2.72 ct
- 10 mm
- Weight: 3.74 ct
- 12 mm
- Weight: 6.46 ct
Topaz against diamond
How wide a round topaz is next to a round diamond of the same weight.
- 0.5 ct
- Topaz: 5.1 mm
- Diamond: 5.1 mm
- Difference: about the same
- 1 ct
- Topaz: 6.4 mm
- Diamond: 6.5 mm
- Difference: about the same
- 2 ct
- Topaz: 8.1 mm
- Diamond: 8.1 mm
- Difference: about the same
- 3 ct
- Topaz: 9.3 mm
- Diamond: 9.3 mm
- Difference: about the same
- 5 ct
- Topaz: 11.0 mm
- Diamond: 11.0 mm
- Difference: about the same
Topaz properties
- Density used in the charts
- Value: 3.53 g/cm3 (range 3.49 to 3.57)
- Hardness (Mohs)
- Value: 8
- Refractive index
- Value: 1.609 to 1.643
Blue topaz is the best-known. Close to diamond in density, so the same weight gives almost the same size.