Diamond Education
MM to Carat Size Chart
Carat is a measure of weight, not size — so two diamonds of the same carat can look quite different depending on their shape. Use the charts below to picture the approximate face-up millimeter dimensions of a diamond at each carat weight.
When you shop for a diamond, carat weight gets most of the attention, but what you actually see on the hand is the stone's millimeter spread — how wide it appears face-up. Elongated shapes like oval, marquise, and pear tend to look larger than a round of the same weight because they carry more of their mass across the surface. The numbers below are approximate: real dimensions vary with cut proportions and depth.
Round & square shapes
A single measurement — the diameter (round) or side length (square shapes), in millimeters.
| Shape | 0.5 ct | 0.75 ct | 1 ct | 1.25 ct | 1.5 ct | 2 ct | 2.5 ct | 3 ct | 4 ct | 5 ct |
|---|---|---|---|---|---|---|---|---|---|---|
| Round | 5.0 | 5.7 | 6.3 | 7.0 | 7.3 | 8.0 | 8.7 | 9.3 | 10.2 | 11.0 |
| Cushion | 4.5 | 5.2 | 5.7 | 6.2 | 6.5 | 7.3 | 8.0 | 8.3 | 9.0 | 10.0 |
| Princess | 4.4 | 5.0 | 5.5 | 5.9 | 6.3 | 7.0 | 7.5 | 8.0 | 8.7 | 9.3 |
| Radiant | 4.3 | 4.9 | 5.5 | 6.0 | 6.5 | 7.0 | 7.5 | 8.0 | 8.8 | 9.5 |
| Asscher | 4.4 | 5.0 | 5.5 | 6.0 | 6.3 | 7.0 | 7.5 | 8.0 | 8.6 | 9.7 |
Values in millimeters (mm).
Elongated shapes
Two measurements — length × width, in millimeters.
| Shape | 0.5 ct | 0.75 ct | 1 ct | 1.25 ct | 1.5 ct | 2 ct | 2.5 ct | 3 ct | 4 ct | 5 ct |
|---|---|---|---|---|---|---|---|---|---|---|
| Oval | 6.5 × 4.5 | 7.4 × 5.2 | 8.0 × 5.5 | 8.8 × 6.0 | 9.0 × 6.5 | 10.0 × 7.0 | 11.0 × 7.5 | 11.5 × 8.0 | 13.0 × 9.0 | 14.0 × 9.5 |
| Emerald | 5.5 × 4.0 | 6.3 × 4.6 | 7.0 × 4.5 | 7.5 × 5.0 | 8.0 × 5.5 | 8.5 × 6.0 | 9.0 × 6.5 | 9.7 × 7.0 | 10.7 × 7.5 | 11.5 × 8.0 |
| Pear | 7.0 × 4.5 | 8.0 × 5.2 | 9.0 × 5.5 | 9.5 × 6.0 | 10.0 × 6.5 | 11.0 × 7.0 | 12.0 × 7.5 | 13.0 × 8.0 | 14.5 × 9.0 | 15.5 × 9.5 |
| Marquise | 8.0 × 4.0 | 9.2 × 4.6 | 10.5 × 5.0 | 11.5 × 5.7 | 11.7 × 6.0 | 13.0 × 6.5 | 14.0 × 7.0 | 15.0 × 7.5 | 16.5 × 8.3 | 17.7 × 9.0 |
| Heart | 5.5 × 5.0 | 6.3 × 5.7 | 7.0 × 6.0 | 7.6 × 6.5 | 8.0 × 7.0 | 9.0 × 8.0 | 9.5 × 8.5 | 10.0 × 9.0 | 11.0 × 10.0 | 12.0 × 10.5 |
Values in millimeters (mm), shown as length × width.
How to use this chart
To gauge how a diamond will look on the hand, measure the width of a finger (or an existing ring's stone) in millimeters and compare it to the figures above. If you love the look of a larger diamond but want to manage budget, an elongated shape or a lower carat weight in a shape with a bigger spread can read larger than its weight suggests.
Ready to see these sizes on a real ring?