Ring size converter
Convert US, UK and EU ring sizes and find your size from the inside diameter or circumference in mm.
- 🇺🇸 US federal & state rules
- ISO 8653 and US ring size formula
- See sources
US ring size
7
17.32 mm inside diameter, 54.4 mm around
- UK / Australia
- N½
- EU / ISO
- 54
- Inside diameter
- 17.32 mm (0.682 in)
- Inside circumference
- 54.4 mm (2.14 in)
Charts vary by a few tenths of a millimeter. A jeweler's gauge is the final check.
Nearby US sizes
| US 6 | 16.51 mm, 51.9 mm around, UK L½, EU 52 |
|---|---|
| US 6.5 | 16.91 mm, 53.1 mm around, UK M½, EU 53 |
| US 7 | 17.32 mm, 54.4 mm around, UK N½, EU 54 |
| US 7.5 | 17.73 mm, 55.7 mm around, UK O½, EU 56 |
| US 8 | 18.13 mm, 57 mm around, UK P½, EU 57 |
- Jewelers' charts can differ by a few tenths of a millimeter, and wide bands fit tighter. Many jewelers suggest going up a quarter or half size for bands wider than 6 mm.
- A string or paper strip around the finger is a rough guide. A jeweler's ring gauge is the most accurate way to size.
Show the math
| Circumference | 54.41 mm |
|---|---|
| Diameter | 54.41 ÷ π = 17.32 mm |
| US size | (17.32 - 11.63) ÷ 0.8128 = 7, nearest quarter 7 |
What to do next
How it works
Every size is turned into the inside circumference in millimeters and then back into each system. US and Canada sizes come from the inside diameter: 11.63 mm plus 0.8128 mm per size, in quarter sizes. UK and Australian letters step by 1.25 mm of circumference, with size C at 40 mm. ISO 8653 sizes, used across Europe, are the circumference itself.
Things to keep in mind
Jewelers' charts are not all identical, and the same size can feel different in a wide band or a comfort-fit band. Knuckles matter too. If the ring has to slide over a large knuckle, size for the knuckle.
Common sizes
| US | UK | EU / ISO | Diameter (mm) | Circumference (mm) |
|---|---|---|---|---|
| 3 | F½ | 44 | 14.1 | 44.2 |
| 4 | H½ | 47 | 14.9 | 46.8 |
| 5 | J½ | 49 | 15.7 | 49.3 |
| 6 | L½ | 52 | 16.5 | 51.9 |
| 6.5 | M½ | 53 | 16.9 | 53.1 |
| 7 | N½ | 54 | 17.3 | 54.4 |
| 7.5 | O½ | 56 | 17.7 | 55.7 |
| 8 | P½ | 57 | 18.1 | 57.0 |
| 9 | R½ | 60 | 18.9 | 59.5 |
| 10 | T½ | 62 | 19.8 | 62.1 |
| 11 | V½ | 65 | 20.6 | 64.6 |
| 12 | X½ | 67 | 21.4 | 67.2 |
| 13 | 70 | 22.2 | 69.7 |
Sources
Rules applied as of 2026-10-19. See the sources below for details.
- ISO 8653:2016 Jewellery, Ring-sizes, Definition, measurement and designationChecked 2026-10-19
- Wikipedia: Ring size (US formula, BS 6820 letter steps, ISO table)Checked 2026-10-19
Frequently asked questions
What is a size 7 ring in mm?
A US 7 has an inside diameter of about 17.3 mm and an inside circumference of about 54.4 mm. That is UK N½ and EU 54.
How do I convert US ring sizes to UK?
Each US size is about 2.55 mm of circumference, and each UK letter is 1.25 mm, so one US size is roughly two UK letters. A US 6 is about UK L½ and a US 8 is about UK P½.
What is the EU or ISO ring size?
ISO 8653 sizes are simply the inside circumference in millimeters. An EU 52 ring measures 52 mm around the inside, which is about a US 6.
How do I measure my ring size at home?
Wrap a strip of paper around the base of your finger, mark where it meets, and measure the length in millimeters. Enter that as the circumference, and measure at the end of the day when fingers are largest.