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Convert ring sizes between US, UK, EU, Japanese, and Swiss sizing systems instantly.
Ring size is a standardized measurement of finger circumference used to ensure a ring fits correctly. The US system uses numbers (1–13), the UK/AU/NZ system uses letters (A–Z), the EU/ISO system uses inside circumference in millimeters, and the Japanese system uses numbers (1–27).
| US | UK | EU (mm) | JP |
|---|---|---|---|
| 5 | J½ | 48 | 9 |
| 6 | L½ | 50.6 | 11 |
| 7 | N½ | 53.1 | 13 |
| 8 | P | 55.7 | 15 |
| 9 | R | 58.3 | 17 |
| 10 | T | 60.8 | 19 |
| 11 | V | 63.4 | 21 |
| 12 | X | 65.9 | 23 |
Formula
Circumference (mm) = Diameter (mm) × πCircumference = the inner circumference of the ring in millimeters (used as the EU/ISO ring size number)
Diameter = the inner diameter of the ring in millimeters
π = pi, approximately 3.14159
Worked Example
18mm diameter finger → ring size
Did you know? The average ring size for women in the US is approximately size 6 (16.5mm diameter), while the average for men is size 10 (19.8mm diameter) (source: American Gem Society).
Sources
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