A 1 carat round diamond measures about 6.44 mm across and covers roughly 32.5 mm² seen from above.
Carat is weight, not size, so the same 1 ct buys visibly different dimensions depending on shape. At this weight the gap between the shape that spreads widest (emerald) and the most compact (cushion) is about 24% of face-up area — for the same weight, and broadly the same price.
| Shape | Length × width (mm) | Face-up area (mm²) |
|---|---|---|
| Round | 6.44 × 6.44 | 32.5 |
| Oval | 7.91 × 5.65 | 35.1 |
| Cushion | 5.84 × 5.56 | 29.0 |
| Pear | 8.44 × 5.44 | 31.3 |
| Marquise | 9.77 × 5.14 | 35.2 |
| Emerald | 7.22 × 5.16 | 36.1 |
| Radiant | 6.39 × 5.33 | 32.8 |
| Princess | 5.49 × 5.49 | 30.1 |
| Asscher | 5.69 × 5.69 | 30.9 |
Face-up area is what the eye reads as "big". Two 1 ct stones can differ by a fifth in the area they cover while weighing exactly the same, because depth hides weight underneath, where nobody sees it.
A figure in millimetres is hard to picture, and photographs of other people's hands are worse than useless — the same stone on a slender finger looks like a bigger stone. This tool renders it at true millimetre scale on a photo of your hand, calibrated from your ring size or a bank card, so the size on screen is the real one. The photo is processed on your device and never uploaded.
See 1 ct on your own hand →