Swiss / IT / ES to Inner diameter (mm) ring size
The short answer
By the formula, Swiss / IT / ES 17 is Inner diameter (mm) 18.1.
Inner circumference 57 mm. Ring sizes are defined by that one measurement, so this conversion is exact up to rounding: US sizes are rounded to the nearest quarter, UK letters to the nearest half.
| Swiss / IT / ES | Inner diameter (mm) |
|---|---|
| 4 | 14.0 |
| 5 | 14.3 |
| 6 | 14.6 |
| 7 | 15.0 |
| 8 | 15.3 |
| 9 | 15.6 |
| 10 | 15.9 |
| 11 | 16.2 |
| 12 | 16.6 |
| 13 | 16.9 |
| 14 | 17.2 |
| 15 | 17.5 |
| 16 | 17.8 |
| 17 | 18.1 |
| 18 | 18.5 |
| 19 | 18.8 |
| 20 | 19.1 |
| 21 | 19.4 |
| 22 | 19.7 |
| 23 | 20.1 |
| 24 | 20.4 |
| 25 | 20.7 |
| 26 | 21.0 |
| 27 | 21.3 |
| 28 | 21.6 |
| 29 | 22.0 |
| 30 | 22.3 |