Ring Size Calculator
Convert between different international ring size standards and find your perfect fit.
How the Ring Size Converter Works
A ring size converter translates a ring size you know, such as a US 7 or a UK N, into the matching size in another system, along with the exact inner diameter and circumference in millimetres. This matters because the US uses numbers, the UK and Australia use letters, and most of Europe sizes rings directly by circumference in millimetres.
Every ring size ultimately comes from one physical measurement: the inside circumference of the band. The US scale increases by about 0.8 mm of diameter per half size, while the EU (ISO) standard simply uses the circumference in millimetres as the size number. Once you know your finger's circumference or diameter, you can find your size anywhere.
Different jewellers may round slightly differently, so treat the chart below as an accurate guide and confirm with a jeweller before ordering an expensive or non-resizable ring.
International Ring Size Chart
This chart matches US, UK and EU ring sizes to inner diameter and circumference. Find your diameter or circumference in millimetres, then read across.
| US | UK | EU | Diameter (mm) | Circumference (mm) |
|---|---|---|---|---|
| 5 | J½ | 49 | 15.7 | 49.3 |
| 6 | L½ | 52 | 16.5 | 51.9 |
| 7 | N½ | 54 | 17.3 | 54.4 |
| 8 | P½ | 57 | 18.1 | 57.0 |
| 9 | R½ | 59 | 19.0 | 59.5 |
| 10 | T½ | 62 | 19.8 | 62.1 |
| 11 | V½ | 64 | 20.6 | 64.6 |
| 12 | X½ | 66 | 21.4 | 67.2 |
The EU size is simply the circumference in millimetres rounded, which is why EU 54 corresponds to a ring measuring about 54 mm around the inside.
How to Measure Your Ring Size at Home
You can measure ring size at home with a strip of paper or an existing ring. For best accuracy, measure at the end of the day when fingers are warm, and avoid measuring when your hands are cold.
Method 1 - measure your finger:
- Wrap a thin strip of paper or string snugly around the base of your finger.
- Mark where the ends overlap and measure that length in millimetres. This is your circumference.
- Match the circumference to the chart above to find your size.
Method 2 - measure a ring that fits:
- Take a ring that already fits the correct finger.
- Measure the inside diameter across the centre in millimetres.
- Match the diameter to the chart to find the equivalent size.
Helpful tips for an accurate fit:
- Measure two or three times and take the average for reliability.
- Account for wider bands, which fit more snugly, so consider going up a half size.
- Make sure the ring can slide over your knuckle, not just the base of the finger.
- Avoid measuring when hot, cold or after exercise, as fingers swell and shrink.
Starting from a millimetre measurement and using the chart as a guide lets you order rings confidently across US, UK and EU systems.
Frequently Asked Questions
UK ring sizes use letters that run roughly half a letter behind each US number. For example, US 6 is about UK L½, US 7 is UK N½, and US 8 is UK P½. Always confirm with a chart for the exact match.
The EU (ISO) ring size is simply the inside circumference of the band in millimetres. So an EU 54 ring measures about 54 mm around the inside, which makes it easy to convert from a millimetre measurement.
Wrap a strip of paper or string around the base of your finger, mark the overlap, and measure the length in millimetres to get the circumference. Alternatively, measure the inside diameter of a ring that already fits and match it to a chart.
Diameter is the straight-line distance across the inside of the ring, while circumference is the distance all the way around the inside. Circumference equals diameter multiplied by about 3.14, and both are used to determine ring size.
Yes. Wide bands sit more snugly because they cover more of the finger, so it is common to go up about a quarter to a half size compared with a thin band for the same comfort.
Measure at the end of the day when your hands are warm and at their largest. Avoid measuring when cold or right after exercise, since fingers can swell or shrink and give an inaccurate size.