Sizing
Ring Size Converter (US, UK, EU, Japan, mm)
Convert a ring size between US, UK letters, EU/ISO, Japanese sizes and inner diameter in mm. Includes a size chart. Free, in your browser.
Result
Your result
- US / Canada
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- UK / Australia
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- EU / ISO (mm)
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- Inner diameter
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- Japan
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Pick the system you know and type the size.
| US | UK | EU / ISO (mm) | Diameter (mm) | Japan |
|---|---|---|---|---|
| 3 | F½ | 44.2 | 14.1 | 4 |
| 4 | H½ | 46.8 | 14.9 | 7 |
| 5 | J½ | 49.3 | 15.7 | 9 |
| 6 | L½ | 51.9 | 16.5 | 12 |
| 7 | N½ | 54.4 | 17.3 | 14 |
| 8 | P½ | 57.0 | 18.1 | 17 |
| 9 | R½ | 59.5 | 18.9 | 20 |
| 10 | T½ | 62.1 | 19.8 | 22 |
| 11 | V½ | 64.6 | 20.6 | 25 |
| 12 | X½ | 67.2 | 21.4 | 27 |
| 13 | — | 69.7 | 22.2 | 30 |
How to use it
- Choose the size system you already know.
- Type the size (a letter for UK, e.g. “N½”).
- Read the equivalents. Use the chart for nearby sizes.
Every system is converted through inner circumference in mm. US size n ≈ diameter 11.63 + 0.8128 × n mm; UK letters start at A ≈ 37.5 mm and add 1.25 mm per letter; EU/ISO is the circumference itself; Japanese sizes are about circumference − 40.
Makers and countries round differently, and wide bands fit tighter. Get measured by a jeweler before ordering an engagement ring.
Frequently asked questions
Questions about this tool
How do I convert a US ring size to UK?
Convert the US size to inner circumference (π × (11.63 + 0.8128 × size) mm), then find the UK letter at that circumference. US 7 is about 54.4 mm, which is close to UK N½.
Is the EU ring size the same as the circumference?
Yes. EU and ISO 8653 sizes are the inner circumference in millimetres, so size 54 means about 54 mm around the inside.