Ring Size Converter
Know a size in one system? Convert it to US, UK, EU, Japanese and Indian sizes in one click — everything goes through millimetres, the one unit every system shares.
Last updated: November 2026
Convert a ring size
Why conversion goes through millimetres
Each country invented its scale separately: the US uses numbers, the UK uses letters, and Europe uses the circumference itself. The reliable route is always the same — turn the size you have into diameter and circumference in mm, then read off every other system. Our US to UK guide explains the letter system in depth.
Ring size conversion at a glance
Full conversion chart
| US / Canada | Diameter (mm) | Circumference (mm) | UK / Australia | EU (ISO) | Japan | India |
|---|---|---|---|---|---|---|
| 3 | 14.1 | 44.2 | F | 44 | 4 | 4 |
| 3.5 | 14.5 | 45.5 | G | 46 | 5 | 5 |
| 4 | 14.9 | 46.8 | H½ | 47 | 7 | 7 |
| 4.5 | 15.3 | 48.0 | I½ | 48 | 8 | 8 |
| 5 | 15.7 | 49.3 | J½ | 49 | 9 | 9 |
| 5.5 | 16.1 | 50.6 | K½ | 51 | 11 | 11 |
| 6 | 16.5 | 51.9 | L½ | 52 | 12 | 12 |
| 6.5 | 16.9 | 53.1 | M½ | 53 | 13 | 13 |
| 7 | 17.3 | 54.4 | N½ | 54 | 14 | 14 |
| 7.5 | 17.7 | 55.7 | O½ | 56 | 15 | 15 |
| 8 | 18.1 | 57.0 | P½ | 57 | 16 | 16 |
| 8.5 | 18.5 | 58.3 | Q½ | 58 | 18 | 18 |
| 9 | 18.9 | 59.5 | R½ | 60 | 19 | 19 |
| 9.5 | 19.4 | 60.9 | S½ | 61 | 20 | 20 |
| 10 | 19.8 | 62.1 | T½ | 62 | 21 | 21 |
| 10.5 | 20.2 | 63.4 | U½ | 63 | 22 | 22 |
| 11 | 20.6 | 64.6 | V½ | 65 | 23 | 23 |
| 11.5 | 21.0 | 66.0 | W½ | 66 | 25 | 25 |
| 12 | 21.4 | 67.2 | X½ | 67 | 26 | 26 |
| 12.5 | 21.8 | 68.5 | Y½ | 69 | 27 | 27 |
| 13 | 22.2 | 69.7 | Z½ | 70 | 29 | 29 |
Full chart, US sizes 3 to 13 in half sizes. EU size is the rounded circumference in mm. Japan and India share the same values on this chart.
Frequently asked questions
How do I convert US to UK ring size?
What is EU ring size?
Popular sizes in detail
One page per size — exact millimetres and inches, every equivalent, and who typically wears it: US 5 · US 6 · US 6.5 · US 7 · US 7.5 · US 8 · US 9 · US 10.