Japan ring sizes
Japanese ring sizes (go) start at 13.0 mm across inside for size 1 and add a third of a millimetre of diameter per size, so Japan 14 is 17.3 mm across and 54.4 mm round, the same as US 7.
No official definition was found. The sizes below follow a simple relation that reproduces the published charts named below within the error stated in the text; use the shop’s own chart when it gives one.
Where it is used: Japan
Japan size table
| Japan size | Inside Ø mm | Circumference mm | Nearest US | Nearest UK | Nearest ISO |
|---|---|---|---|---|---|
| 5 | 14.3 | 45.0 | ≈ 3.25 | G | 45 |
| 6 | 14.7 | 46.1 | 3.75 | ≈ H | 46 |
| 7 | 15.0 | 47.1 | ≈ 4.25 | ≈ H½ | 47 |
| 8 | 15.3 | 48.2 | 4.5 | I½ | ≈ 48 |
| 9 | 15.7 | 49.2 | 5 | ≈ J½ | ≈ 49 |
| 10 | 16.0 | 50.3 | ≈ 5.5 | ≈ K | ≈ 50 |
| 11 | 16.3 | 51.3 | 5.75 | L | ≈ 51 |
| 12 | 16.7 | 52.4 | 6.25 | M | ≈ 52 |
| 13 | 17.0 | 53.4 | ≈ 6.5 | ≈ M½ | ≈ 53 |
| 14 | 17.3 | 54.5 | 7 | N½ | ≈ 54 |
| 15 | 17.7 | 55.5 | ≈ 7.5 | O½ | ≈ 56 |
| 16 | 18.0 | 56.5 | ≈ 7.75 | ≈ P | ≈ 57 |
| 17 | 18.3 | 57.6 | 8.25 | Q | ≈ 58 |
| 18 | 18.7 | 58.6 | ≈ 8.75 | R | ≈ 59 |
| 19 | 19.0 | 59.7 | ≈ 9 | ≈ S | ≈ 60 |
| 20 | 19.3 | 60.7 | 9.5 | S½ | ≈ 61 |
| 21 | 19.7 | 61.8 | ≈ 10 | T½ | ≈ 62 |
| 22 | 20.0 | 62.8 | 10.25 | ≈ U½ | ≈ 63 |
| 23 | 20.3 | 63.9 | 10.75 | V | 64 |
| 24 | 20.7 | 64.9 | ≈ 11 | W | 65 |
| 25 | 21.0 | 66.0 | 11.5 | ≈ X | 66 |
| 26 | 21.3 | 67.0 | ≈ 12 | X½ | 67 |
| 27 | 21.7 | 68.1 | ≈ 12.25 | Y½ | 68 |
| 28 | 22.0 | 69.1 | 12.75 | ≈ Z½ | 69 |
| 29 | 22.3 | 70.2 | ≈ 13.25 | ≈ Z+1 | ≈ 70 |
| 30 | 22.7 | 71.2 | ≈ 13.5 | Z+2 | ≈ 71 |
About Japan sizes
Japan ring sizes are commonly called go sizes, and the system is used in Japan. For example, Japan 14 matches US 7 in the table, with an inside diameter of 17.3 mm and a circumference of 54.4 mm.
The go scale is a trade convention, not an official definition found in the cited materials. Japan also has an industrial standard described as following the ISO method, which uses whole millimetres of circumference. Do not rely on the shortcut that adds 40 to a go size: it is 1.2 mm off at go 30.
Use the table to compare Japan sizes with the other systems and the measurements inside a ring. Before buying, check the shop's own chart and measure a ring that fits. The RingSteps converter and printable sizer can also help you compare sizes.
Sources
- Ring (指輪): size standard JIS S 4700 and the go scale (Wikipedia (Japanese)) Checked November 10, 2026
- Ring size table, go 1 to 30 (moocota) Checked November 10, 2026
- Ring size chart (PDF), go 1 to 30 (Itokawa) Checked November 10, 2026