CM to Ring Size
If you've measured your finger with paper or string, here's how that centimetre figure becomes a ring size.
A finger's circumference in mm equals the EU ring size (ISO 8653). So 5.2 cm = 52 mm = EU 52 ≈ US 6. Multiply your cm reading by 10, then read across the chart.
How to measure in cm
- Wrap a thin strip of paper or string around the base of the finger — snug, where the ring will sit.
- Mark where the end overlaps, then lay it flat against a ruler.
- Read the length in cm. That's your inner circumference — multiply by 10 for mm.
CM / mm to ring size chart
| Circ. (cm) | Circ. (mm) | Diameter (mm) | US | UK | EU |
|---|---|---|---|---|---|
| 4.7 | 46.8 | 14.8 | 4 | H | 47 |
| 4.8 | 48 | 15.2 | 4.5 | I | 48 |
| 4.9 | 49.3 | 15.7 | 5 | J½ | 49 |
| 5.1 | 50.6 | 16.1 | 5.5 | L | 51 |
| 5.2 | 51.9 | 16.5 | 6 | M | 52 |
| 5.3 | 53.1 | 16.9 | 6.5 | N | 53 |
| 5.4 | 54.4 | 17.3 | 7 | O | 54 |
| 5.6 | 55.7 | 17.7 | 7.5 | P | 56 |
| 5.7 | 57 | 18.1 | 8 | Q | 57 |
| 5.8 | 58.3 | 18.5 | 8.5 | Q½ | 58 |
| 6.0 | 59.5 | 19 | 9 | R½ | 59 |
| 6.1 | 60.8 | 19.4 | 9.5 | S½ | 61 |
| 6.2 | 62.1 | 19.8 | 10 | T½ | 62 |
| 6.3 | 63.4 | 20.2 | 10.5 | U½ | 63 |
| 6.5 | 64.6 | 20.6 | 11 | V½ | 65 |
Inner circumference of the band. If you measured diameter instead, multiply by π (≈3.14) to get circumference.
FAQ
How do I convert cm to a ring size?
Measure the inside circumference of the finger or a ring in centimetres, multiply by 10 to get millimetres, and match it to the chart. A 5.2 cm (52 mm) circumference is about a US 6 / EU 52.
Is ring size based on circumference or diameter?
Both describe the same band. EU sizes equal the inner circumference in millimetres (ISO 8653); US/UK sizes are a separate scale. The chart lists both so you can match whichever you measured.
How do I measure my finger in cm?
Wrap a thin strip of paper or string around the base of the finger, mark where it overlaps, and measure the length in cm with a ruler. That length is the inner circumference.
What if my measurement is between two sizes?
Round up to the larger size — a ring that's slightly loose is far easier to wear (and to resize down) than one that won't pass the knuckle.
EU ring size = inner circumference in mm (ISO 8653). US/UK figures are standard conversions; band fit varies slightly by maker.