Ring Size Converter
Enter the inner circumference of a ring in millimetres to get its diameter and matching US, UK and EU sizes.
Result
How to use
- Enter your values in the fields above.
- Press Calculate to see your result instantly.
- Use the Share button to copy a link to your result.
About this calculator
This calculator converts a ring's inner circumference (in millimetres) into its inner diameter, then matches that diameter against US numeric sizes, UK letter sizes, and EU sizes — the three main ring-sizing systems used by jewelers around the world, which don't line up on a simple formula and instead follow standardized lookup tables.
Online shoppers use it to convert a measured string or paper strip wrapped around a finger into a size they can order confidently, and anyone buying a ring as a surprise gift uses it to convert a sized ring borrowed from the recipient into the right number to order.
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