Size charts
Ring Size Calculator
Compare a ring’s inside diameter or finger circumference with a published US size reference.
Tiffany US ring size reference
Inside measurements in millimetres. The calculator chooses the next listed size when your measurement falls between rows.
| US size | Inside diameter (mm) | Circumference (mm) |
|---|---|---|
| 3 | 14.1 | 44.2 |
| 3.5 | 14.5 | 45.5 |
| 4 | 14.9 | 46.8 |
| 4.5 | 15.3 | 48 |
| 5 | 15.7 | 49.3 |
| 5.5 | 16.1 | 50.6 |
| 6 | 16.5 | 51.9 |
| 6.5 | 16.9 | 53.1 |
| 7 | 17.3 | 54.4 |
| 7.5 | 17.7 | 55.7 |
| 8 | 18.1 | 57 |
| 8.5 | 18.5 | 58.3 |
| 9 | 18.9 | 59.5 |
| 9.5 | 19.4 | 60.8 |
| 10 | 19.8 | 62.1 |
| 10.5 | 20.2 | 63.4 |
| 11 | 20.6 | 64.6 |
| 11.5 | 21 | 65.9 |
| 12 | 21.4 | 67.2 |
| 12.5 | 21.8 | 68.5 |
| 13 | 22.2 | 69.7 |
A few helpful details
Good to know
Why does the tool round up between sizes?
This follows the named reference guide’s advice to choose the larger size between two sizes. A jeweller should confirm an expensive or hard-to-resize purchase.
Can I measure an image on my screen?
No. Zoom, scaling and display size make screen measurements unreliable. Use an actual measurement or an in-person fitting.
Is this an international size conversion?
No. The result is a US reference size with inside diameter and circumference. It does not infer UK letters or claim every jeweller uses identical dimensions.
Reference: Tiffany ring sizing guide (opens in a new tab) · Reference checked October 2026.