Millimetres to US ring size converter
If you have measured a finger or an existing ring in millimetres, you can convert straight to a US size. Inner circumference maps directly: about 51.8 mm is a US 6 and 54.4 mm is a US 7. If you measured the diameter instead, multiply by π (3.1416) to get circumference, or just use the tool below.
Quick answer
A mm 54.4 is 7 in US (about 54.4 mm inner circumference). Use the converter for your exact size, or the chart below for the full range.
Between two sizes? Size up for a comfortable fit, see how to measure accurately.
mm → US at a glance
- 46.7 mm = 4
- 49.3 mm = 5
- 51.8 mm = 6
- 54.4 mm = 7
- 56.9 mm = 8
- 59.5 mm = 9
- 62.0 mm = 10
- 64.6 mm = 11
mm to US ring size chart
| mmCircumference | USUS / Canada | mmDiameter |
|---|---|---|
| 46.7 | 4 | 14.9 |
| 48.0 | 4½ | 15.3 |
| 49.3 | 5 | 15.7 |
| 50.5 | 5½ | 16.1 |
| 51.8 | 6 | 16.5 |
| 53.1 | 6½ | 16.9 |
| 54.4 | 7 | 17.3 |
| 55.6 | 7½ | 17.7 |
| 56.9 | 8 | 18.1 |
| 58.2 | 8½ | 18.5 |
| 59.5 | 9 | 18.9 |
| 60.7 | 9½ | 19.3 |
| 62.0 | 10 | 19.7 |
| 63.3 | 10½ | 20.1 |
| 64.6 | 11 | 20.5 |
| 65.8 | 11½ | 21.0 |
| 67.1 | 12 | 21.4 |
Common questions
How do I convert a mm ring size to US?
Enter your mm size in the converter above and read the US result, or find your row in the chart below. Every value is calculated from the ring’s inner circumference, so it works in both directions.
What is a mm 54.4 in US?
A mm 54.4 is 7 in US. That ring has an inner circumference of about 54.4 mm.
Related conversions
Or see the full ring size chart.