Ring Sizes Around ISO 66
| US | UK | ISO / EU | JP / KR | Diameter (mm) | Circumference (mm) |
| 10 | T | 62 | 21 | 19.8 | 62.1 |
| 10.5 | U | 63 | 23 | 20.2 | 63.4 |
| 11 | V | 65 | 24 | 20.6 | 64.6 |
| 11.5 | W | 66 | 25 | 21 | 65.9 |
| 12 | X | 67 | 26 | 21.4 | 67.2 |
| 12.5 | Y | 68 | 27 | 21.8 | 68.5 |
| 13 | Z | 70 | 28 | 22.2 | 69.7 |
Frequently Asked Questions
Does ISO 66 round up or down in US?
Round to pass the knuckle; a large band that grips the base but sticks at the joint is uncomfortable and a resizing job jewellers would rather avoid.
See a number that looks off? Report an error on this page.