EU / ISO to Inner diameter (mm) ring size
The short answer
By the formula, EU / ISO 57 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.
| EU / ISO | Inner diameter (mm) |
|---|---|
| 44 | 14.0 |
| 45 | 14.3 |
| 46 | 14.6 |
| 47 | 15.0 |
| 48 | 15.3 |
| 49 | 15.6 |
| 50 | 15.9 |
| 51 | 16.2 |
| 52 | 16.6 |
| 53 | 16.9 |
| 54 | 17.2 |
| 55 | 17.5 |
| 56 | 17.8 |
| 57 | 18.1 |
| 58 | 18.5 |
| 59 | 18.8 |
| 60 | 19.1 |
| 61 | 19.4 |
| 62 | 19.7 |
| 63 | 20.1 |
| 64 | 20.4 |
| 65 | 20.7 |
| 66 | 21.0 |
| 67 | 21.3 |
| 68 | 21.6 |
| 69 | 22.0 |
| 70 | 22.3 |