Ring Size Converter
US, UK, EU, Japan & mm.
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About Ring Size Converter
Convert ring sizes between US/Canada, UK/Australia, EU (ISO) and Japan — or from a diameter or circumference in millimetres, and back again. Enter a size in any system (or a measurement) and see every equivalent at once, with a full chart below.
The EU column follows the ISO 8653 standard (size = inner circumference in mm). It is completely free with no sign-up, and it runs entirely in your browser.
Frequently asked questions
- What is a US 7 ring size in the UK and EU?
- A US 7 is about a UK N½ and an EU (ISO) 54, with an inside diameter of roughly 17.3 mm. Enter any size in the tool to see all the equivalents at once.
- How do I convert a ring size from millimetres?
- Choose 'Diameter (mm)' or 'Circumference (mm)' as your input and type the measurement — the tool finds the closest standard ring size and shows every system's equivalent.
- Which EU ring size system does this use?
- The EU column uses ISO 8653, where the size equals the ring's inner circumference in millimetres. Some French and continental charts number rings differently, so when in doubt match by diameter or circumference.
- How can I measure my ring size at home?
- Measure the inside diameter of a ring that already fits, in millimetres, and enter it as the diameter — or wrap a strip of paper around your finger, mark it, and measure the length as the circumference.
- What if I'm between two sizes?
- Size up rather than down, and measure at the end of the day when fingers are at their largest, since a ring that's slightly loose is far easier to wear than one that's too tight.