Reference · Updated June 2026
Ring size reference
A complete cross-reference of ring sizes between the US, UK, EU and Japanese systems — with inner diameter and circumference in millimetres so you can size a ring you already own.
| US | UK | EU | JP | Ø (mm) | Circ. (mm) |
|---|---|---|---|---|---|
| 4 | H | 47 | 7 | 14.9 | 46.8 |
| 4.5 | I | 48 | 8 | 15.3 | 48.0 |
| 5 | J 1/2 | 49 | 9 | 15.7 | 49.3 |
| 5.5 | K 1/2 | 50 | 10 | 16.1 | 50.6 |
| 6 | L 1/2 | 51.5 | 11 | 16.5 | 51.8 |
| 6.5 | M 1/2 | 53 | 12 | 16.9 | 53.1 |
| 7 | N 1/2 | 54 | 13 | 17.3 | 54.4 |
| 7.5 | O 1/2 | 55.5 | 14 | 17.7 | 55.7 |
| 8 | P 1/2 | 57 | 16 | 18.2 | 57.0 |
| 8.5 | Q 1/2 | 58 | 17 | 18.6 | 58.3 |
| 9 | R 1/2 | 59 | 18 | 19.0 | 59.5 |
| 9.5 | S 1/2 | 61 | 19 | 19.4 | 60.8 |
| 10 | T 1/2 | 62 | 20 | 19.8 | 62.1 |
| 10.5 | U 1/2 | 63 | 22 | 20.2 | 63.4 |
| 11 | V 1/2 | 64.5 | 23 | 20.6 | 64.6 |
| 12 | X 1/2 | 67 | 25 | 21.4 | 67.2 |
| 13 | Z 1/2 | 69 | 27 | 22.2 | 69.7 |
Measure an existing ring
Place a ring you already wear on a ruler and measure the inner diameter in millimetres. Look up the diameter column to find your size in every system.
Measure your finger
Wrap a strip of paper around the base of your finger, mark where it overlaps, and measure that length in millimetres — that's your circumference.
Measure at the end of the day
Fingers swell up to 5% over the course of a day and with temperature. Always measure when warm and at the end of the day for the most reliable fit.
Knuckle versus base
If your knuckle is significantly larger than your finger base, size up. Most jewellers recommend a fit that slides over the knuckle with mild resistance.
Common questions
- Are UK and US ring sizes the same?
- No. UK uses letters (H, J 1/2, etc.) while the US uses half-step numerics. A US 6 is roughly a UK L 1/2.
- Is the EU number my circumference?
- Yes — EU ring sizes correspond closely to the inner circumference of the band in millimetres. EU 54 ≈ 54 mm inner circumference.