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Follow channelRing Size Converter: Diameter and Circumference in mm to US, UK, EU and Japan
Enter the inside diameter or circumference in mm, or your size in any system, to get the US, UK, EU (ISO) and Japanese size, plus how to measure your finger with a paper strip and a printable ruler.
Measure your finger at home
- Cut a thin paper strip (about 5 mm) and wrap it around the base of the finger, snug but comfortable.
- Mark where the ends meet, flatten it and measure in mm: that is the circumference.
- Make sure it will pass the knuckle. Measure late in the day at a normal temperature; fingers swell a little in heat.
- Or measure the inside diameter of a ring that fits you, edge to edge.
Printable ruler (120 mm)
Print at 100% scale (no "fit to page"), then check with a real ruler that 0–100 is exactly 10 cm before using it.
Size chart
| Diameter (mm) | Circumference (mm) | US | UK | EU / ISO | JP |
|---|---|---|---|---|---|
| 14.07 | 44.2 | 3 | F | 44 | 4 |
| 14.48 | 45.5 | 3 ½ | G | 46 | — |
| 14.88 | 46.8 | 4 | H | 47 | 7 |
| 15.29 | 48.0 | 4 ½ | I | 48 | 8 |
| 15.7 | 49.3 | 5 | J½ | 49 | 9 |
| 16.1 | 50.6 | 5 ½ | K½ | 51 | 10 |
| 16.51 | 51.9 | 6 | L½ | 52 | 11 |
| 16.92 | 53.1 | 6 ½ | M½ | 53 | 13 |
| 17.32 | 54.4 | 7 | N½ | 54 | 14 |
| 17.73 | 55.7 | 7 ½ | O½ | 56 | 15 |
| 18.14 | 57.0 | 8 | P½ | 57 | 16 |
| 18.54 | 58.3 | 8 ½ | Q¼ | 58 | 17 |
| 18.95 | 59.5 | 9 | R½ | 60 | 18 |
| 19.35 | 60.8 | 9 ½ | S½ | 61 | 19 |
| 19.76 | 62.1 | 10 | T½ | 62 | 20 |
| 20.17 | 63.4 | 10 ½ | U½ | 63 | 22 |
| 20.57 | 64.6 | 11 | V½ | 65 | 23 |
| 20.98 | 65.9 | 11 ½ | W½ | 66 | 24 |
| 21.39 | 67.2 | 12 | X½ | 67 | 25 |
| 21.79 | 68.5 | 12 ½ | Y½ | 68 | 26 |
| 22.2 | 69.7 | 13 | Z½ | 70 | 27 |
How it works
The EU size in ISO 8653 is the inside circumference in mm. Other systems come from the conversion table published on Wikipedia (US sizes step 0.8128 mm in diameter per size). The tool finds the closest row to your number.
Sources
- Wikipedia: Ring size (conversion table) — diameter, circumference, US/UK/Japan
- ISO 8653: Jewellery — Ring-sizes — size = inside circumference in mm
Sources checked: 2026-10-25
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FAQ
I am EU 54, what is that in US?
About 54 mm circumference is US 7, UK N½ and JP 14 in the chart.
Diameter or circumference?
Circumference is easier for a finger (paper strip); diameter is easier for an existing ring. The tool takes both.
What if I am between two sizes?
Usually go up, especially for wide bands, which need more room.