💍 Ring Size Converter
Convert a ring size across US/Canada, UK/Australia, EU/ISO, and Japan — plus inside diameter and circumference in millimetres. Enter what you know in any one system and read every other.
💍 Your ring size in every system
Matched to the nearest standard size (US 6). Ring sizes vary slightly between charts and makers — for an expensive ring, confirm with a jeweller before you buy.
Full conversion chart
| US / CA | UK / AU | EU / ISO | Japan | Diameter | Circumference |
|---|---|---|---|---|---|
| 3 | F | 44 | 4 | 14.1 mm | 44.2 mm |
| 3.5 | G | 45 | 5 | 14.5 mm | 45.5 mm |
| 4 | H | 47 | 7 | 14.9 mm | 46.8 mm |
| 4.5 | I | 48 | 8 | 15.3 mm | 48.0 mm |
| 5 | J | 49 | 9 | 15.7 mm | 49.3 mm |
| 5.5 | K | 51 | 10 | 16.1 mm | 50.6 mm |
| 6 | L | 52 | 12 | 16.5 mm | 51.9 mm |
| 6.5 | M | 53 | 13 | 16.9 mm | 53.1 mm |
| 7 | N | 54 | 14 | 17.3 mm | 54.4 mm |
| 7.5 | O | 56 | 15 | 17.7 mm | 55.7 mm |
| 8 | P | 57 | 16 | 18.1 mm | 57.0 mm |
| 8.5 | Q | 58 | 17 | 18.5 mm | 58.3 mm |
| 9 | R | 60 | 18 | 19.0 mm | 59.5 mm |
| 9.5 | S | 61 | 19 | 19.4 mm | 60.8 mm |
| 10 | T | 62 | 20 | 19.8 mm | 62.1 mm |
| 10.5 | U | 63 | 22 | 20.2 mm | 63.4 mm |
| 11 | V | 65 | 23 | 20.6 mm | 64.6 mm |
| 11.5 | W | 66 | 24 | 21.0 mm | 65.9 mm |
| 12 | X | 67 | 25 | 21.4 mm | 67.2 mm |
| 12.5 | Y | 69 | 26 | 21.8 mm | 68.5 mm |
| 13 | Z | 70 | 27 | 22.2 mm | 69.7 mm |
One finger, four number systems
The United States and Canada size rings on a numeric scale, the UK and Australia use letters, continental Europe uses the inside circumference in millimetres (ISO 8653), and Japan runs its own JIS numbers. The physical ring never changes — only the label does — so the honest way to convert is through the one thing they all describe: the inside of the band.
That is why this tool always shows the inside diameter and circumference alongside the regional sizes. Measure the band you have, or the finger you are buying for, and every system falls out of the same measurement. The relationship between the two is simply circumference = π × diameter.
❓ Frequently Asked Questions
How do I convert my ring size between US, UK, EU, and Japanese sizes?
Enter the size you already know in one system and this converter reads every other system off a standard jewellers' chart. For example, a US 6 is a UK L, an EU/ISO 52, and a Japanese 12, with an inside diameter of about 16.5 mm and a circumference of about 51.9 mm.
What is the difference between EU size and inside circumference?
They are almost the same thing. Under ISO 8653 the EU ring size IS the inside circumference of the band in millimetres, so an EU 52 ring measures roughly 52 mm around the inside. That is why EU sizes look so different from US or UK sizes.
How do I measure my ring size at home?
Wrap a strip of paper or string around the base of your finger, mark where it overlaps, and measure that length in millimetres — that is your inside circumference. Or measure the inside diameter of a ring that already fits. Enter either here to get the size in every system. The relationship is circumference = π × diameter.
Why do ring size charts differ slightly?
There is no single global standard, so charts round diameter and circumference a little differently and map UK letters to US numbers with small variations. This tool matches to the nearest standard size. For an engagement ring or anything costly, confirm the size with a jeweller before ordering.
Does a wide band change the size I need?
Yes. Wide or thick bands sit more snugly, so many jewellers suggest going up a quarter to a half size for bands wider than about 6 mm. Cold fingers also run smaller. Measure at the end of the day when your hands are warm for the most representative fit.