Japan measures rings in 号 (gō). Each 号 is a fixed inner diameter, so it maps exactly to an inner circumference in mm — and approximately to a US ring size.
| JP 号 | Inner circumference (mm) | Inner diameter (mm) | US (approx.) |
|---|---|---|---|
| 1 | 40.8 | 13.0 | 1.5 |
| 2 | 41.9 | 13.3 | 2 |
| 3 | 42.9 | 13.7 | 2.5 |
| 4 | 44.0 | 14.0 | 3 |
| 5 | 45.0 | 14.3 | 3.5 |
| 6 | 46.1 | 14.7 | 4 |
| 7 | 47.1 | 15.0 | 4 |
| 8 | 48.2 | 15.3 | 4.5 |
| 9 | 49.2 | 15.7 | 5 |
| 10 | 50.3 | 16.0 | 5.5 |
| 11 | 51.3 | 16.3 | 6 |
| 12 | 52.4 | 16.7 | 6 |
| 13 | 53.4 | 17.0 | 6.5 |
| 14 | 54.5 | 17.3 | 7 |
| 15 | 55.5 | 17.7 | 7.5 |
| 16 | 56.5 | 18.0 | 8 |
| 17 | 57.6 | 18.3 | 8.5 |
| 18 | 58.6 | 18.7 | 8.5 |
| 19 | 59.7 | 19.0 | 9 |
| 20 | 60.7 | 19.3 | 9.5 |
| 21 | 61.8 | 19.7 | 10 |
| 22 | 62.8 | 20.0 | 10.5 |
| 23 | 63.9 | 20.3 | 10.5 |
| 24 | 64.9 | 20.7 | 11 |
| 25 | 66.0 | 21.0 | 11.5 |
| 26 | 67.0 | 21.3 | 12 |
| 27 | 68.1 | 21.7 | 12.5 |
| 28 | 69.1 | 22.0 | 13 |
| 29 | 70.2 | 22.3 | 13 |
| 30 | 71.2 | 22.7 | 13.5 |
号 and the inner circumference are exact (circumference = π × inner diameter). The US size is approximate.
Japanese ring size 号 (gō) is defined by the ring’s inner diameter: 号1 is 13.0 mm across and every step adds 1/3 mm, so the inner circumference (π × diameter) is exact. The US column is approximate — US sizes fall between Japanese 号 values.
The inner circumference in mm is the reliable figure to match against a ring you own. The US size is approximate because the two scales do not line up on whole numbers.
Approximate — brands vary. The Japanese figure (cm foot length, or 号) is the reliable one.
← All Japanese size converters · Japanese units converter
Japanese 号 (gō) is set by inner diameter — 号1 is 13.0 mm across and each step adds 1/3 mm. Match the inner circumference in mm of a ring that fits you to the chart to read off the 号.
The Japanese and US ring scales use different steps, so US sizes do not line up on whole 号 numbers. The US column here is the closest approximate value.
