Diamond Sizing Guide
How big is a one carat diamond
Round diamonds are measured across in millimetres. Here is what each size looks like on a hand, and how it relates to carat weight.
On the hand
Round diamonds
To scale
Screens vary. Hold a credit card next to the chart: it is 85.6 mm wide.
Millimetres to carats
| Across (mm) | Round, about (ct) |
|---|---|
| 3 | 0.10 |
| 4 | 0.25 |
| 4.5 | 0.33 |
| 5 | 0.50 |
| 5.5 | 0.66 |
| 6 | 0.75 |
| 6.5 | 1.00 |
| 7 | 1.25 |
| 7.4 | 1.50 |
| 8.1 | 2.00 |
Approximate, for round brilliant cuts. Ovals and marquise look larger for the same weight.
See them in person
A free 20-minute sizing session with a bridal expert, comparison stones side by side. Your appointment is confirmed when we reply.
