Ring size chart
A US size 7 is 17.3 mm in diameter and 54.4 mm in circumference — EU 54, roughly UK N, Japan 14. The table below converts every standard size from US 3 to US 13, including half sizes.
| US / Canada | Inside diameter (mm) | Inside circumference (mm) | EU (ISO 8653) | UK / AU (approx.) | Japan |
|---|---|---|---|---|---|
| 3 | 14.1 | 44.2 | 44 | F | 4 |
| 3.5 | 14.5 | 45.5 | 46 | G | 5.5 |
| 4 | 14.9 | 46.8 | 47 | H | 7 |
| 4.5 | 15.3 | 48.0 | 48 | I | 8 |
| 5 | 15.7 | 49.3 | 49 | J | 9 |
| 5.5 | 16.1 | 50.6 | 51 | K | 10.5 |
| 6 | 16.5 | 51.9 | 52 | L | 12 |
| 6.5 | 16.9 | 53.1 | 53 | M | 13 |
| 7 | 17.3 | 54.4 | 54 | N | 14 |
| 7.5 | 17.7 | 55.7 | 56 | O | 15 |
| 8 | 18.1 | 57.0 | 57 | P | 16 |
| 8.5 | 18.5 | 58.3 | 58 | Q | 17 |
| 9 | 19.0 | 59.5 | 60 | R | 18 |
| 9.5 | 19.4 | 60.8 | 61 | S | 19 |
| 10 | 19.8 | 62.1 | 62 | T | 20 |
| 10.5 | 20.2 | 63.4 | 63 | U | 21.5 |
| 11 | 20.6 | 64.6 | 65 | V | 23 |
| 11.5 | 21.0 | 65.9 | 66 | W | 24 |
| 12 | 21.4 | 67.2 | 67 | X | 25 |
| 12.5 | 21.8 | 68.5 | 69 | Y | 26 |
| 13 | 22.2 | 69.7 | 70 | Z | 27 |
EU sizes follow ISO 8653, where the size number is the ring's inner circumference in millimetres. UK letter sizes are the widely used jeweller approximations and may differ slightly from one jeweller to another. Half sizes between whole sizes are interpolated.
How to read this chart
Diameter is the straight-line distance across the inside of the band; circumference is the distance around that inside edge. The two are linked by π, so either measurement finds your row. EU sizes are the circumference itself under ISO 8653 — an EU 57 is a ring measuring 57.0 mm around. UK letters are a jeweller's convention and only approximate: two reputable charts can place the same ring a fraction of a letter apart, which is why this site always shows the millimetre measurements alongside the letter.
Half sizes matter more than they look. A half US size is only about 0.4 mm of diameter, but that is roughly the difference between a ring that slides over the knuckle with slight resistance — the correct fit — and one that spins or sticks.
Frequently asked questions
What ring size is 18 mm?
An inside diameter of 18 mm sits between US 7.5 (17.7 mm) and US 8 (18.1 mm). At 18.0 mm the circumference is about 56.5 mm (EU 56–57), and most people this measurement fits best in a US 8.
What is the most common ring size?
For women, US 6 is the most commonly purchased size; for men it is around US 9–10. See the average ring size page for the fuller picture.
Do wide bands need a bigger size?
Usually yes. Bands wider than about 6 mm sit on a fleshier part of the finger and feel tighter, so many jewellers suggest going up a quarter to a half size compared with a narrow band.
Need your size first? Measure with a strip of paper, measure a ring on screen, or print a ring sizer.