US to UK 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.
Numbers on one hand, letters on the other
The US ring scale counts in halves and the UK scale answers with one lettered step for each of them, so the alphabet climbs in lockstep with the numbers. On this chart US 8.5 lines up with UK Q.
American ring sizes count in numbers and half numbers, while Britain letters its scale from A upward, so the two run alongside each other with one lettered step for each half number. Both ultimately describe the same thing, the inside of the band, which the ISO scale states directly as a circumference in millimetres. A jeweller's rule of thumb sits behind the chart: a wide band is usually taken up about half a size, and a finger swings close to a full size between a cold morning and a warm afternoon, so measure warm and late.
Common questions
Does each US half-size equal one UK letter?
Yes. The scales step together, so moving up half a US size advances the UK size by one letter across the chart.
When should I measure my finger?
Warm and late in the day. Fingers shrink in the cold, and a band measured on a cold morning can bind by afternoon.
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.