Ring Size Converter
Convert ring sizes between US, UK, EU, and Japanese systems.
Also shows inner diameter and circumference in mm.
Type in any field — the others update instantly. Sizes are approximate.
Ring sizes are based on the inner circumference of the ring.
US/Canada sizes use a numbered scale (typically 3–16). UK/Australia uses letters (A–Z+). EU/ISO uses the inner circumference in millimeters. Japan uses a numbered scale (1–30).
Conversion formulas (using inner circumference in mm):
- US size = (circumference_mm − 36.5) / 2.55
- EU size = circumference_mm (rounded to nearest 0.25)
- Japan size = (circumference_mm − 38.0) / 0.8333
- Diameter (mm) = circumference_mm / π
Common reference sizes:
| US | UK | EU (mm) | Japan | Diameter (mm) |
|---|---|---|---|---|
| 5 | J½ | 49.3 | 9 | 15.7 |
| 6 | L½ | 51.8 | 12 | 16.5 |
| 7 | N½ | 54.4 | 14 | 17.3 |
| 8 | P½ | 57.0 | 16 | 18.1 |
| 9 | R½ | 59.5 | 19 | 18.9 |
| 10 | T½ | 62.1 | 21 | 19.8 |
Note: Sizes are approximate. Manufacturing tolerances and different standards may cause slight variations.