Ring Size Converter

How ring sizing works

Ring size is based on the inner circumference (or diameter) of the ring, matched to the circumference of your finger where the ring will sit. Different countries use different numbering systems for the same physical size.

How this calculator works

This calculator converts between circumference and diameter using Circumference = π × Diameter, then estimates US ring size from circumference using the standard relationship of about 2.55mm of circumference per US half-size (anchored at US size 3 = 44.2mm). The EU (French) size shown is approximately equal to the circumference in millimeters, which is how most European charts number rings.

For the most accurate result, measure an existing ring that already fits well (inner diameter), or wrap a strip of paper or string snugly around your finger and measure its length for circumference, ideally at the end of the day when fingers are largest.

Ring sizing can vary slightly between jewelers and band widths (wider bands typically need to be sized up slightly), so use this as a reliable estimate and confirm with in-person sizing when possible.