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International ring size converter
Pick the system you know and the size you wear. The converter shows the same ring in six systems plus exact millimetres.
- US / Canada
- 7
- UK / Australia
- N½
- EU / ISO
- 54
- Japan / China
- 14
- India
- 14
- Italy / Spain / CH
- 14
- Inside diameter
- 17.3 mm
- Circumference
- 54.4 mm
- Diameter (in)
- 0.682″
The size ladder: why one US size is two UK letters
Every system measures the same thing, the inside of the ring, but each climbs with a different rung spacing. Step up and down the US scale and compare how far each system moves.
51.9 mm around (16.51 mm across). One size smaller was 49.3 mm, so this step added 2.55 mm.
- US
- 6
- +1 size = +0.81 mm across
- UK
- L½
- +1 letter = +1.25 mm around
- EU
- 52
- +1 = +1 mm around
- JP
- 11
- uneven steps
2.55 mm per US size ÷ 1.25 mm per UK letter ≈ 2.04, so UK letters move about twice as fast. Over ten US sizes, that 0.04 drift adds up, which is why no simple "add N letters" rule works across the whole range.
US to EU ring sizes
| US | EU |
|---|---|
| 5 | 49 |
| 6 | 52 |
| 7 | 54 |
| 8 | 57 |
| 9 | 60 |
| 10 | 62 |
US to Japanese ring sizes
| US | Japan |
|---|---|
| 4 | 7 |
| 5 | 9 |
| 6 | 11 |
| 7 | 14 |
| 8 | 16 |
| 9 | 18 |
| 10 | 20 |
The formulas behind the conversions
- US / Canada: inside diameter (mm) = 11.63 + 0.8128 × size.
- EU / ISO 8653: size = inside circumference in mm.
- UK / Australia (BS 6820): C = 40 mm circumference, each letter adds 1.25 mm; half letters in between.
- Italy / Spain / Switzerland: circumference − 40.
- Japan / China, India: non-linear; looked up from the standard equivalency table.
Need the letters in detail? See the UK to US ring size table. For every quarter size at once, open the full ring size chart.
Questions people ask
How do I convert a US ring size to EU?
Work out the inside circumference: diameter = 11.63 + 0.8128 × US size (mm), circumference = diameter × π. The EU size is that circumference rounded to the nearest millimetre. US 7 → 17.32 mm × π = 54.4 mm → EU 54.
What is a US 6 in UK sizes?
US 6 is UK L½ (51.9 mm inside circumference). US 7 is N½ and US 8 is P½.
Is European ring size the same in every country?
Most of continental Europe (France, Germany, Belgium, Austria, the Nordics) uses ISO 8653, where the size is the circumference in mm. Italy, Spain and Switzerland use the same measurement minus 40, so ISO 54 is Italian 14.
Why do different converter charts disagree by half a size?
Some charts round differently, some copy older tables, and some brands run large or small. This converter calculates from the published standards; for Japanese and Indian sizes it uses the standard equivalency table.