Tourmaline size chart: carat to mm for every shape
By HeyGema™ · Updated
In short
A 1 carat round tourmaline measures about 6.8 mm across, against 6.5 mm for a 1 carat diamond. Tourmaline is lighter than diamond (3.06 against 3.52), so the same weight gives a bigger stone, 5% wider across.
- 6.8 mm1 carat round tourmaline
- 3.06density, g/cm3
- 7 to 7.5hardness, Mohs
Carat to mm calculator
About 6.8 x 6.8 mm
An estimate for a well-cut stone. A deep or shallow cut faces up smaller or bigger.
Tourmaline size chart: carat to mm
Face-up length and width in mm of a well-cut tourmaline at each weight and shape. Tourmaline is lighter than diamond (3.06 against 3.52), so the same weight gives a bigger stone, 5% wider across.
| Weight | Round | Oval | Cushion | Emerald cut | Pear | Princess |
|---|---|---|---|---|---|---|
| 0.25 ct | 4.3 | 5.3 x 3.6 | 3.7 x 3.7 | 4.6 x 3.3 | 5.6 x 3.6 | 3.6 x 3.6 |
| 0.5 ct | 5.4 | 6.7 x 4.6 | 4.7 x 4.7 | 5.8 x 4.2 | 7.1 x 4.6 | 4.6 x 4.6 |
| 0.75 ct | 6.1 | 7.6 x 5.2 | 5.3 x 5.3 | 6.7 x 4.8 | 8.1 x 5.2 | 5.2 x 5.2 |
| 1 ct | 6.8 | 8.4 x 5.8 | 5.9 x 5.9 | 7.3 x 5.2 | 8.9 x 5.8 | 5.8 x 5.8 |
| 1.5 ct | 7.7 | 9.6 x 6.6 | 6.7 x 6.7 | 8.4 x 6.0 | 10.2 x 6.6 | 6.6 x 6.6 |
| 2 ct | 8.5 | 10.6 x 7.3 | 7.4 x 7.4 | 9.2 x 6.6 | 11.2 x 7.3 | 7.3 x 7.3 |
| 3 ct | 9.7 | 12.1 x 8.3 | 8.5 x 8.5 | 10.6 x 7.6 | 12.8 x 8.3 | 8.3 x 8.3 |
| 4 ct | 10.7 | 13.3 x 9.1 | 9.3 x 9.3 | 11.6 x 8.3 | 14.1 x 9.1 | 9.1 x 9.1 |
| 5 ct | 11.6 | 14.3 x 9.9 | 10.0 x 10.0 | 12.5 x 9.0 | 15.2 x 9.9 | 9.9 x 9.9 |
| 10 ct | 14.6 | 18.1 x 12.4 | 12.6 x 12.6 | 15.8 x 11.3 | 19.2 x 12.4 | 12.4 x 12.4 |
Length x width in mm. A round stone shows one number, its diameter.
mm to carat for a round tourmaline
If you know the size, this is the weight. Measure across the widest point of the stone, face up.
- 4 mm
- Weight: 0.21 ct
- 5 mm
- Weight: 0.4 ct
- 6 mm
- Weight: 0.7 ct
- 7 mm
- Weight: 1.11 ct
- 8 mm
- Weight: 1.66 ct
- 9 mm
- Weight: 2.36 ct
- 10 mm
- Weight: 3.24 ct
- 12 mm
- Weight: 5.6 ct
Tourmaline against diamond
How wide a round tourmaline is next to a round diamond of the same weight.
- 0.5 ct
- Tourmaline: 5.4 mm
- Diamond: 5.1 mm
- Difference: +0.2 mm
- 1 ct
- Tourmaline: 6.8 mm
- Diamond: 6.5 mm
- Difference: +0.3 mm
- 2 ct
- Tourmaline: 8.5 mm
- Diamond: 8.1 mm
- Difference: +0.4 mm
- 3 ct
- Tourmaline: 9.7 mm
- Diamond: 9.3 mm
- Difference: +0.4 mm
- 5 ct
- Tourmaline: 11.6 mm
- Diamond: 11.0 mm
- Difference: +0.5 mm
Tourmaline properties
- Density used in the charts
- Value: 3.06 g/cm3 (range 3.00 to 3.10)
- Hardness (Mohs)
- Value: 7 to 7.5
- Refractive index
- Value: 1.614 to 1.666
Many colors, from pink rubellite to green verdelite. Lighter than diamond, so it faces up bigger.