Ring Size Converter
Convert a ring size between US numbers, UK letters, European (ISO) circumference and inside diameter. Useful when buying rings from another country.
How to use the Ring Size Converter
- Choose the system you know.
- Enter your size (for UK, a letter such as L or L½).
- Read the equivalent sizes.
How it works
US ring sizes increase by about 0.8128 mm in inside diameter per whole size, starting from about 11.63 mm at size 0. EU/ISO sizes are simply the inside circumference in millimeters, and UK letters step by half a letter for each quarter-ish US size. Fingers swell in heat and in the evening, so measure at the end of the day.
Ring size chart
| US | UK | EU / ISO | Diameter (mm) |
|---|---|---|---|
| 3 | F½ | 44.2 | 14.07 |
| 4 | H½ | 46.8 | 14.88 |
| 5 | J½ | 49.3 | 15.69 |
| 5.5 | K½ | 50.6 | 16.1 |
| 6 | L½ | 51.9 | 16.51 |
| 6.5 | M½ | 53.1 | 16.91 |
| 7 | N½ | 54.4 | 17.32 |
| 7.5 | O½ | 55.7 | 17.73 |
| 8 | P½ | 57 | 18.13 |
| 9 | R½ | 59.5 | 18.95 |
| 10 | T½ | 62.1 | 19.76 |
| 11 | V½ | 64.6 | 20.57 |
| 12 | X½ | 67.2 | 21.38 |
Frequently asked questions
What is the most common ring size?
For women, US 6–7; for men, US 9–10.
What is a US 7 in UK sizes?
A US 7 is about a UK N½, with an inside diameter of about 17.3 mm.
Should a wide band be a bigger size?
Yes — bands wider than about 6 mm usually need a quarter to half size larger.