Ring Size Converter
Use this ring size converter to translate a ring size between the US/Canada, UK/Australia, European (ISO) and Japanese systems. Buying a ring from overseas or sizing a gift? Enter the size in whichever system you know and get the equivalents in the others, plus the inside diameter in millimetres.
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Convert your ring size
Enter values above and press Calculate to see your result.
Formula used
Ring sizes all describe the band's inside size, just on different scales:
- US/Canada — a number where each full size ≈ 0.81 mm of diameter.
- UK/Australia — letters A–Z (with half sizes).
- EU/ISO — the inside circumference in millimetres.
- Japan — its own numbered scale.
The US size relates to inside diameter by diameter (mm) ≈ 11.63 + 0.8128 × US size, and circumference = π × diameter.
Worked examples
US 7 ≈ UK N, EU 54, JP 14, inside diameter ≈ 17.3 mm.
UK L ≈ US 6, EU 51.5.
EU 60 ≈ US ~9.25.
How to use this calculator
- Choose the system you already know the size in.
- Enter the size — a number for US/EU/JP, a letter for UK.
- Press Calculate to see the size in every system and the diameter.
- If you're between sizes or have wide knuckles, size up slightly.
Ring size conversion chart
| US | UK | EU | Japan | Diameter (mm) |
|---|---|---|---|---|
| 5 | J | 49 | 9 | 15.7 |
| 6 | L | 51.5 | 12 | 16.5 |
| 7 | N | 54 | 14 | 17.3 |
| 8 | P | 57 | 16 | 18.1 |
| 9 | R | 59 | 18 | 19.0 |
| 10 | T | 62 | 20 | 19.8 |
Sizes are matched to the nearest standard; brands differ slightly.
Who should use this converter
Anyone buying a ring from an international seller, sizing an engagement or wedding ring, or shopping for a gift where the size is known in a different country's system. It's also useful for matching a vintage or inherited ring to a modern size chart.
How to find your ring size
- Use an existing ring that fits the right finger and measure its inside diameter (see our diameter tool).
- Get measured at a jeweller for the most reliable result.
- Measure at the end of the day, when fingers are largest, and at a normal temperature.
Tips for a good fit
A ring should slide on with light resistance and need a gentle tug over the knuckle. Wide bands fit tighter, so size up about half a size for bands over ~6 mm. Cold shrinks fingers and heat swells them, so avoid measuring at extremes.
Limitations of this converter
National systems don't line up perfectly, so conversions are matched to the nearest standard size and may be half a size out between brands. For an expensive or permanent purchase, confirm with the jeweller's own sizing and, ideally, a physical sizer.
Frequently asked questions
What is US ring size 7 in UK and EU?
US 7 is approximately UK N and EU (ISO) 54, with an inside diameter of about 17.3 mm.
How do European ring sizes work?
EU/ISO sizes are simply the ring's inside circumference in millimetres, so EU 54 means a 54 mm inside circumference.
Are ring size conversions exact?
No system lines up perfectly, so conversions round to the nearest standard size. For important purchases, confirm with the jeweller.
Should I size up for a wide band?
Yes — wide bands fit more snugly. Go up about half a size for bands wider than roughly 6 mm.
Does finger size change during the day?
Yes. Fingers are smallest when cold or in the morning and largest in heat or at day's end. Measure at a normal temperature, later in the day.