UK / AU to Inner diameter (mm) ring size
The short answer
By the formula, UK / AU P is Inner diameter (mm) 17.9.
Inner circumference 56.3 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.
| UK / AU | Inner diameter (mm) |
|---|---|
| F | 13.9 |
| G | 14.3 |
| H | 14.7 |
| I | 15.1 |
| J | 15.5 |
| K | 15.9 |
| L | 16.3 |
| M | 16.7 |
| N | 17.1 |
| O | 17.5 |
| P | 17.9 |
| Q | 18.3 |
| R | 18.7 |
| S | 19.1 |
| T | 19.5 |
| U | 19.9 |
| V | 20.3 |
| W | 20.7 |
| X | 21.1 |
| Y | 21.5 |
| Z | 21.9 |