Measure a ring you own. Take a ring that fits the same finger and measure its inside diameter in millimeters.
Or measure your finger. Wrap a thin strip of paper around the base of the finger, mark the overlap, and measure the length in millimeters.
| US size | Diameter | Around |
|---|
| 4 | 14.9 mm | 46.8 mm |
| 4.5 | 15.3 mm | 48.0 mm |
| 5 | 15.7 mm | 49.3 mm |
| 5.5 | 16.1 mm | 50.6 mm |
| 6 | 16.5 mm | 51.9 mm |
| 6.5 | 16.9 mm | 53.1 mm |
| 7 | 17.3 mm | 54.4 mm |
| 7.5 | 17.7 mm | 55.7 mm |
| 8 | 18.1 mm | 57.0 mm |
| 8.5 | 18.5 mm | 58.3 mm |
| 9 | 19.0 mm | 59.5 mm |
| 9.5 | 19.4 mm | 60.8 mm |
| 10 | 19.8 mm | 62.1 mm |
| 10.5 | 20.2 mm | 63.4 mm |
| 11 | 20.6 mm | 64.6 mm |
| 12 | 21.4 mm | 67.2 mm |
Measure at the end of the day, when fingers are largest. Between sizes, or choosing a wide band? Go up half a size. Or try the ring on in person before you buy.
