Utility Loft → Diamond Size → Carat to MM
Carat to MM Converter
Convert a round diamond's carat weight to its millimeter diameter — and back. Enter a carat or a mm size below.
Face-up diameter—
Enter a carat weight above to see the diameter in millimeters.
Carat to mm chart (round)
| Carat | Diameter (mm) | Inches |
|---|---|---|
| 0.25 | 4.1 | 0.16 |
| 0.33 | 4.5 | 0.18 |
| 0.50 | 5.2 | 0.20 |
| 0.75 | 5.9 | 0.23 |
| 1.00 | 6.5 | 0.26 |
| 1.25 | 7.0 | 0.28 |
| 1.50 | 7.4 | 0.29 |
| 1.75 | 7.8 | 0.31 |
| 2.00 | 8.2 | 0.32 |
| 2.50 | 8.8 | 0.35 |
| 3.00 | 9.4 | 0.37 |
For round brilliants. mm ≈ 6.5 × ∛carat; exact size varies with cut. Other shapes differ — see the by-shape chart.
Related
Frequently asked questions
What is 1 carat in mm?
A round 1.00 carat diamond is about 6.5 mm in diameter. For other shapes the millimeters differ even at the same carat weight.
What is 0.5 carat in mm?
A round 0.50 carat diamond is about 5.2 mm across.
How do you calculate mm from carat?
For round diamonds, diameter scales with the cube root of weight: mm ≈ 6.5 × ∛carat. That's because weight grows with volume, so doubling the diameter multiplies the weight roughly eightfold.