Size guides › Carat to millimeters
Diamond size chart
How big is a diamond, in millimeters?
Carat measures weight, not size. Two stones of the same carat can look noticeably different on a hand, because shape and depth decide how that weight is spread. Here's every shape at every common weight.
1 carat in every shape, to scale
Length × width, in millimeters
Area seen from above, in mm²
This is the number that decides how large a stone looks. Read across a row: at the same weight, elongated shapes spread wider than a round, while deep shapes hide weight underneath.
| Weight | Round | Oval | Cushion | Pear | Marquise | Emerald | Radiant | Princess | Asscher |
|---|---|---|---|---|---|---|---|---|---|
| 0.25 ct | 12.9 | 13.9 | 11.5 | 13.1 | 14.0 | 14.3 | 13.0 | 11.9 | 12.3 |
| 0.50 ct | 20.5 | 22.1 | 18.3 | 20.8 | 22.2 | 22.7 | 20.7 | 19.0 | 19.4 |
| 0.75 ct | 26.8 | 29.0 | 24.0 | 27.3 | 29.1 | 29.8 | 27.1 | 24.8 | 25.5 |
| 1.00 ct | 32.5 | 35.1 | 29.0 | 33.0 | 35.2 | 36.1 | 32.8 | 30.1 | 30.9 |
| 1.25 ct | 37.7 | 40.8 | 33.7 | 38.3 | 40.9 | 41.9 | 38.1 | 34.9 | 35.8 |
| 1.50 ct | 42.6 | 46.0 | 38.0 | 43.3 | 46.2 | 47.3 | 43.0 | 39.4 | 40.5 |
| 2.00 ct | 51.6 | 55.8 | 46.1 | 52.5 | 55.9 | 57.3 | 52.1 | 47.8 | 49.0 |
| 2.50 ct | 59.9 | 64.7 | 53.5 | 60.9 | 64.9 | 66.4 | 60.4 | 55.4 | 56.9 |
| 3.00 ct | 67.6 | 73.1 | 60.4 | 68.7 | 73.3 | 75.0 | 68.2 | 62.6 | 64.2 |
Every figure is calculated by the same functions the tool uses, from standard per-shape weight factors and typical proportions. Real stones vary — a certificate gives the actual measurements of a particular diamond, and those are what to use when it matters.
A table can't show you your hand
It can tell you a stone is 7.91 × 5.65 mm. The tool shows you what that looks like on your own finger.