UK to ISO Ring Size Chart
| US | UK | ISO / EU | JP / KR | Diameter (mm) | Circumference (mm) |
|---|---|---|---|---|---|
| 3 | F | 44 | 4 | 14.1 | 44.2 |
| 3.5 | G | 46 | 5 | 14.5 | 45.5 |
| 4 | H | 47 | 7 | 14.9 | 46.8 |
| 4.5 | I | 48 | 8 | 15.3 | 48 |
| 5 | J | 49 | 9 | 15.7 | 49.3 |
| 5.5 | K | 51 | 10 | 16.1 | 50.6 |
| 6 | L | 52 | 12 | 16.5 | 51.9 |
| 6.5 | M | 53 | 13 | 16.9 | 53.1 |
| 7 | N | 54 | 14 | 17.3 | 54.4 |
| 7.5 | O | 56 | 15 | 17.7 | 55.7 |
| 8 | P | 57 | 16 | 18.1 | 57 |
| 8.5 | Q | 58 | 18 | 18.6 | 58.3 |
| 9 | R | 60 | 19 | 18.9 | 59.5 |
| 9.5 | S | 61 | 20 | 19.4 | 60.8 |
| 10 | T | 62 | 21 | 19.8 | 62.1 |
| 10.5 | U | 63 | 23 | 20.2 | 63.4 |
| 11 | V | 65 | 24 | 20.6 | 64.6 |
| 11.5 | W | 66 | 25 | 21 | 65.9 |
| 12 | X | 67 | 26 | 21.4 | 67.2 |
| 12.5 | Y | 68 | 27 | 21.8 | 68.5 |
| 13 | Z | 70 | 28 | 22.2 | 69.7 |
| 13.5 | Z1 | 71 | 28+ | 22.6 | 71 |
| 14 | Z2 | 72 | 28+ | 23 | 72.3 |
ISO, EU, France and Germany all label rings by the inner circumference in millimetres, so the ISO / EU number is the same across Continental Europe. Japan (号) and Korea (호) share one scale. JP sizes above 28 are approximate.
British letters against the millimetre scale
ISO is not an offset of the UK scale, it is the ring's inner circumference in millimetres set by ISO 8653. Each step up the UK column adds about 1 mm of circumference, so UK Q works out to ISO 58 on the table above.
The British alphabet scale and the ISO millimetre scale describe the same band from two directions: one lettered step corresponds to a small, fixed gain in circumference under ISO 8653. Reading the letters as millimetres removes the guesswork, and it explains why Continental European rings, which are labelled by that same circumference, slot straight onto the ISO column. Sizing to the measurement rather than the letter also handles the practical traps: a wide band takes up about half a size, and warm fingers read larger than cold ones.
Common questions
How much circumference is one UK letter?
A small, steady step under ISO 8653, which the table reads out in millimetres so a letter becomes a measurement.
Can I use a UK size for a ring bought in Europe?
Convert through the ISO millimetre column. Continental rings are labelled by that circumference, so the mm figure is the common ground.
Ring size charts · How to measure ring size · Ring sizes around the world · Printable ring sizer
Sources
Ring circumference standard: ISO 8653:2016.
Japanese and Korean ring scale: rings data pack, mother-tongue sources.