Ring Size Calculator

What this calculator does

Ring size can be estimated from finger circumference or the inner diameter of a ring that already fits. Temperature, time of day and ring width can all affect comfort.

Formula used

Diameter is converted to circumference using pi. The calculator then finds the nearest size in a comparison table.

How to read the result

Wider bands often need a slightly larger size. For valuable jewellery, use this as a first check and confirm with a jeweller or a physical ring sizer.

Assumptions

• Uses millimetres.
• Returns nearest table match.
• Does not account for band width or finger swelling.

Sources and checks

This calculator uses a standard public formula. Where rules or thresholds can change, source links are listed on the relevant page.

Frequently asked questions