Gemstones
Carat to MM Converter (Round Diamond Size)
See the approximate diameter of a round brilliant diamond for any carat weight, with a size chart from 0.25 to 3 carats. Free, in your browser.
Result
Your result
- Approximate diameter
- —
- Approximate depth
- —
Enter a carat weight.
| Carat | Diameter (mm) |
|---|---|
| 0.25 | 4.1 |
| 0.50 | 5.1 |
| 0.75 | 5.9 |
| 1.00 | 6.5 |
| 1.50 | 7.4 |
| 2.00 | 8.1 |
| 2.50 | 8.8 |
| 3.00 | 9.3 |
How to use it
- Enter the carat weight.
- Read the approximate diameter and depth.
- Compare with the chart to picture nearby sizes.
Reverses the round estimation formula (carat = diameter² × depth × 0.0061) assuming a depth of 61% of the diameter.
Deep or shallow cuts look smaller or larger for the same weight. Other shapes are not covered here.
Frequently asked questions
Questions about this tool
How many mm is a 1 carat diamond?
A well-cut 1 carat round brilliant is about 6.4–6.5 mm across. Deeper cuts are narrower for the same weight.
Why do two diamonds of the same carat look different in size?
Carat is weight, not size. Cut proportions decide how much of that weight shows as diameter.