Ring size chart
| Circumference (mm) | Diameter (mm) | US | UK | EU |
|---|---|---|---|---|
| 44.2 | 14.1 | 3 | F | 44 |
| 46.8 | 14.9 | 4 | H | 47 |
| 49.3 | 15.7 | 5 | J½ | 49 |
| 51.9 | 16.5 | 6 | L½ | 52 |
| 54.4 | 17.3 | 7 | N½ | 54 |
| 57.0 | 18.1 | 8 | P½ | 57 |
| 59.5 | 18.9 | 9 | R½ | 59 |
| 62.1 | 19.8 | 10 | T½ | 62 |
| 64.6 | 20.6 | 11 | V½ | 65 |
| 67.2 | 21.4 | 12 | X½ | 67 |
Fingers swell. They are largest in the late afternoon and in warm weather, and smallest first thing on a cold morning — the difference can be a full half size. Measure warm and late, and if the knuckle is noticeably larger than the base of the finger, size to slide over the knuckle rather than to fit the base snugly.
Ring size is set by the inside circumference of the band. A 54 mm circumference is a US 7, a UK N½, and an EU 54 — the European scale is simply the circumference in millimetres, which makes it the easiest to reason about.
How to measure ring size
The four scales are unrelated systems rather than conversions of each other, which is why the numbers look arbitrary. EU sizing is the circumference in millimetres. Japan uses its own numeric scale. US sizes step in quarters from a base, and UK sizes use letters with half sizes between them. Only the physical measurement is common to all four, which is why every reliable conversion starts by measuring in millimetres rather than translating between the scales directly.
Questions
Wrap paper around the finger base, mark the overlap, and measure the length in millimetres. That is the circumference.