Ring Size Converter
US ring sizes map to inner circumference (and diameter). This chart uses common jewelry values. Finger size changes with temperature and time of day — measure more than once.
Inner diameter17.3 mm
Inner circumference54.3 mm
Approximate.
Formula
Approximate diameter (mm) ≈ 14.1 + 0.8 × (US size − 3).
How to use this calculator
- Enter US size.
- Read diameter and circumference.
- A jeweler’s mandrel is more accurate.
Examples
US 7
About 17.3 mm diameter, 54 mm circumference.
FAQ
UK letters?+
UK uses letters. Convert via circumference if you have a sizing strip in mm.