German and Dutch jewellers quote the inside diameter in millimetres directly, and EU sizes are the circumference in millimetres.
Ring size chart
| US & Canada | UK & Australia | EU / ISO | Swiss / IT / ES | Japan | Diameter (mm) | Circumference (mm) |
|---|---|---|---|---|---|---|
| 3 | F½ | 44 | 4 | 4 | 14.1 | 44.2 |
| 3½ | G½ | 45 | 5 | 5 | 14.5 | 45.5 |
| 4 | H½ | 47 | 7 | 7 | 14.9 | 46.8 |
| 4½ | I½ | 48 | 8 | 8 | 15.3 | 48.0 |
| 5 | J½ | 49 | 9 | 9 | 15.7 | 49.3 |
| 5½ | K½ | 51 | 11 | 10 | 16.1 | 50.6 |
| 6 | L½ | 52 | 12 | 12 | 16.5 | 51.9 |
| 6½ | M½ | 53 | 13 | 13 | 16.9 | 53.1 |
| 7 | N½ | 54 | 14 | 14 | 17.3 | 54.4 |
| 7½ | O½ | 56 | 16 | 15 | 17.7 | 55.7 |
| 8 | P½ | 57 | 17 | 16 | 18.1 | 57.0 |
| 8½ | Q½ | 58 | 18 | 18 | 18.5 | 58.2 |
| 9 | R½ | 60 | 20 | 19 | 18.9 | 59.5 |
| 9½ | S½ | 61 | 21 | 20 | 19.4 | 60.8 |
| 10 | T½ | 62 | 22 | 21 | 19.8 | 62.1 |
| 10½ | U½ | 63 | 23 | 22 | 20.2 | 63.3 |
| 11 | V½ | 65 | 25 | 24 | 20.6 | 64.6 |
| 11½ | W½ | 66 | 26 | 25 | 21.0 | 65.9 |
| 12 | X½ | 67 | 27 | 26 | 21.4 | 67.2 |
| 12½ | Z | 68 | 28 | 27 | 21.8 | 68.5 |
| 13 | Z+1 | 70 | 30 | 29 | 22.2 | 69.7 |
How the sizes are defined
RingSizeChart converts every size to the inside circumference in millimetres and finds the nearest size in each system:
- US and Canada: size 0 is 0.458 in (11.63 mm) across and each size adds 0.032 in (0.8128 mm), in quarter sizes. Circumference is about 36.5 mm + 2.55 mm × size.
- UK, Ireland, Australia and New Zealand (BS 6820): letters with half sizes, 1.25 mm of circumference per letter from A = 37.5 mm to Z = 68.75 mm, then Z+1, Z+2 and so on.
- EU / ISO 8653: the inside circumference in mm, so size 54 is 54 mm around. Used in France, Belgium, Austria and the Nordic countries.
- Switzerland, Italy and Spain: the circumference minus 40 mm, so size 14 is 54 mm.
- Germany and the Netherlands: the inside diameter in mm.
- Japan: the customary scale, 13 mm across for size 1 and ⅓ mm more per size. Japanese and Asian retailers' charts can differ by a size.
Sizes in different systems rarely line up exactly, and jewellers' charts differ by up to half a size. Fit also depends on band width, comfort-fit profiles and temperature. For an expensive ring, have your finger sized by a jeweller.
Frequently asked questions
What ring size is 18 mm diameter?
About US 7¾ to 8 (56.5 mm around).
What ring size is 16 mm?
About US 5½ (50.3 mm around).
What ring size is 20 mm?
About US 10¼ (62.8 mm around).
Is RingSizeChart free?
Yes, with no sign-up or ads.
Is my size saved?
Yes, in this browser only.