Convert finger circumference in mm to US, UK, and EU ring sizes. Free online ring size converter with international size chart and FAQ.
The ring size calculator converts your finger circumference measurement (in millimeters) to ring sizes in US, UK, and EU standards. This is essential for online ring shopping, gift buying, and ensuring a perfect fit without visiting a jeweler.
US Size ≈ (Circumference(inches) - 1.72) / 0.032
Diameter = Circumference / π
EU Size ≈ Circumference(mm) + 2US ring sizes are based on the inner circumference in inches, with each size incrementing by approximately 0.032 inches. UK sizes use a letter system (A through Z). EU sizes are approximately equal to the circumference in millimeters minus 40 plus 42. These are approximations; actual sizes may vary slightly by jeweler.
| Input | Output |
|---|---|
| 54 mm circumference | US: 7 | UK: O | EU: 56 | Diameter: 17.2 mm |
| 49 mm circumference | US: 5 | UK: J | EU: 51 | Diameter: 15.6 mm |
| 60 mm circumference | US: 10 | UK: T | EU: 62 | Diameter: 19.1 mm |