Ring Size Converter → MM to Ring Size Converter
MM to Ring Size Converter
Enter a ring's inside diameter in millimeters to see your size across every standard. If you measured the circumference instead, switch tabs above.
Your US size—
Enter a measurement above to see your size in every standard.
MM to Ring Size chart
| Diameter (mm) | US / CA | UK / AU | Europe | Japan |
|---|---|---|---|---|
| 14.1 | 3 | F | 44 | 4 |
| 14.5 | 3.5 | G | 45½ | 5 |
| 14.9 | 4 | H½ | 47 | 7 |
| 15.3 | 4.5 | I½ | 48 | 8 |
| 15.7 | 5 | J½ | 49 | 9 |
| 16.1 | 5.5 | K½ | 50½ | 10 |
| 16.5 | 6 | L½ | 52 | 11 |
| 16.9 | 6.5 | M½ | 53 | 12 |
| 17.3 | 7 | N½ | 54 | 13 |
| 17.7 | 7.5 | O½ | 55½ | 14 |
| 18.1 | 8 | P½ | 57 | 16 |
| 18.5 | 8.5 | Q½ | 58 | 17 |
| 19.0 | 9 | R½ | 59½ | 18 |
| 19.4 | 9.5 | S½ | 61 | 19 |
| 19.8 | 10 | T½ | 62 | 20 |
| 20.2 | 10.5 | U½ | 63½ | 22 |
| 20.6 | 11 | V½ | 65 | 23 |
| 21.0 | 11.5 | W½ | 66 | 24 |
| 21.4 | 12 | Y | 67½ | 25 |
| 21.8 | 12.5 | Z | 68½ | 26 |
| 22.2 | 13 | Z+1 | 70 | 27 |
Industry-standard approximations; manufacturers vary slightly. If you're between sizes, round up.
FAQ
What ring size is 18mm?
An inside diameter of 18 mm is approximately a US size 8 (UK P½, EU 57). Use the tool above for the exact match to your measurement.
What is the difference between diameter and circumference in mm?
Diameter is the straight-across inside width; circumference is the distance around the inside (diameter × π). European sizes are the circumference in mm, so a 54 EU ring is 54 mm around the inside.