Online Tool Store
Ring Size Converter
Convert a ring size between US/Canada, UK/Australia, EU, and internal diameter in millimeters, shown side by side. Runs entirely in your browser.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Example shown - pick your own size, or measure your finger diameter in mm below.
UK / Australia
EU size
Diameter
How the ring size converter works
- Select your known US/Canada ring size.
- The tool looks up the matching UK/Australia letter size, EU numeric size, and internal diameter in millimeters.
- Use the millimeter diameter if you're ordering from a jeweler that only lists measurements.
FAQ
How do I measure my ring size at home?
Wrap a strip of paper or string around your finger, mark where it overlaps, measure that length, and divide by π (3.14159) to get the internal diameter in millimeters - then match it to the closest size here.
Why do UK sizes use letters instead of numbers?
The UK, Australia, and several Commonwealth countries use an alphabetical sizing system (A through Z, with half sizes) rather than the numeric systems used in the US or continental Europe.
Does ring width affect the size I should order?
Yes, slightly. Wider bands (over about 6mm) can feel tighter than a thin band of the same labeled size, so some jewelers recommend going up half a size for wide rings.
Which sizing system does the EU use?
EU (and many European countries) size rings by the internal circumference in millimeters, which is why EU sizes are larger numbers than US or UK sizes for the same physical ring.
How we compare
| Feature | Online Tool Store | Printable ring sizer chart | Jeweler's size chart page |
|---|---|---|---|
| No printing required | ✓ | ✗ | ✓ |
| Four systems shown at once | ✓ | Varies | Often just one or two |
| No sign-up or ads | ✓ | ✓ | ✗ |
For a quick cross-reference across four sizing systems without printing anything, Ring Size Converter gets you there instantly.