International ring size chart
US 3–13 across five systems, with calculated diameter and circumference in millimetres. International equivalents are approximate; see the methodology for rounding and source limits.
Swipe or scroll sideways to compare every column.
| US / CA | UK / AU | EU / ISO | Japan | CH / IT / ES | Inner diameter, millimetres | Circ mm | Ø in |
|---|---|---|---|---|---|---|---|
| 3 | F½ | 44 | 4 | 4 | 14.07 | 44.2 | 0.554 |
| 3.5 | G½ | 45 | 5 | 5 | 14.48 | 45.5 | 0.570 |
| 4 | H½ | 47 | 7 | 7 | 14.88 | 46.8 | 0.586 |
| 4.5 | I½ | 48 | 8 | 8 | 15.29 | 48.0 | 0.602 |
| 5 | J½ | 49 | 9 | 9 | 15.70 | 49.3 | 0.618 |
| 5.5 | K½ | 51 | 10 | 11 | 16.10 | 50.6 | 0.634 |
| 6 | L½ | 52 | 12 | 12 | 16.51 | 51.9 | 0.650 |
| 6.5 | M½ | 53 | 13 | 13 | 16.92 | 53.1 | 0.666 |
| 7 | N½ | 54 | 14 | 14 | 17.32 | 54.4 | 0.682 |
| 7.5 | O½ | 56 | 15 | 16 | 17.73 | 55.7 | 0.698 |
| 8 | P½ | 57 | 16 | 17 | 18.14 | 57.0 | 0.714 |
| 8.5 | Q½ | 58 | 17 | 18 | 18.54 | 58.3 | 0.730 |
| 9 | R½ | 60 | 18 | 20 | 18.95 | 59.5 | 0.746 |
| 9.5 | S½ | 61 | 19 | 21 | 19.35 | 60.8 | 0.762 |
| 10 | T½ | 62 | 20 | 22 | 19.76 | 62.1 | 0.778 |
| 10.5 | U½ | 63 | 22 | 23 | 20.17 | 63.4 | 0.794 |
| 11 | V½ | 65 | 23 | 25 | 20.57 | 64.6 | 0.810 |
| 11.5 | W½ | 66 | 24 | 26 | 20.98 | 65.9 | 0.826 |
| 12 | Y | 67 | 25 | 27 | 21.39 | 67.2 | 0.842 |
| 12.5 | Z | 68 | 26 | 28 | 21.79 | 68.5 | 0.858 |
| 13 | Z½ | 70 | 27 | 30 | 22.20 | 69.7 | 0.874 |
How to read this chart
Find the size you know in its column, then read across for the equivalents. If you measured a finger or an existing ring in millimetres, match the Ø mm (inner diameter) or Circ mm (inner circumference) column. If your measurement falls between rows, use the interactive converter.
Notes on accuracy
- EU/ISO numbers are the inner circumference in mm (ISO 8653).
- UK uses half letters (US 7 = UK N½); whole-letter charts are often off by a size.
- Japan, India and China are lookup-based and can differ by up to a full size between charts.
- Switzerland / Italy / Spain ≈ circumference in mm minus 40.
Frequently asked questions
What size is a 17 mm ring?
A 17.3 mm inner diameter is a US 7 (UK N½, EU 54). 17 mm is just under US 7 — closest to US 6.75–7.
Does EU ring size equal the circumference?
Yes. Under ISO 8653 the EU/ISO size number is the inner circumference in millimetres, so EU 54 means a 54 mm circumference.
Why do UK sizes use half letters like N½?
US whole sizes fall between UK whole letters, so the accurate UK equivalent is usually a half letter. Charts that show only whole letters are often wrong by up to a full size.