Japanese Ring Size to US Converter
Japanese ring sizes are written as a number with 号 (gō), from 1 to about 30. Each step is about 1/3 mm wider than the last, which is smaller than a US half size. As a rule of thumb, Japanese 9 ≈ US 5, 11 ≈ US 5¾, 13 ≈ US 6½.
Japanese ring size chart
Inner diameter and circumference in millimeters. US sizes are rounded to the nearest quarter size.
How Japanese ring sizes work
- Most shops use the JCS scale (Japan Jewelry Council standard): size 1 has an inner diameter of 13.0 mm, and each size adds 1/3 mm.
- If you see a big number like 50号, the shop is probably using the JIS scale, where the number is the inner circumference in mm. Use "From mm → inner circumference" above.
- Japanese steps are finer than US steps. One US full size is about 2.4 Japanese sizes, so you will often land between two Japanese sizes.
- EU (ISO) sizes are the inner circumference in mm, so they are easy to compare.
How to measure your ring size
- Take a ring that fits the finger you want and measure the inside diameter in mm with a ruler. Measure across the widest point.
- Or wrap a strip of paper around the finger, mark where it overlaps, and measure the length. That is the circumference. Paper and string can stretch, so treat it as a rough guide.
- Measure at the end of the day, when fingers are slightly bigger, and not when your hands are cold.
- For a wide band (about 4 mm or more), go up about one Japanese size, because wide rings feel tighter.
Common questions
What is a Japanese size 9 in US size?
About US 5. Japanese 9 has an inner diameter of 15.67 mm, and US 5 is 15.70 mm.
What is US size 7 in Japanese ring size?
About Japanese 14. US 7 is 17.32 mm, and Japanese 14 is 17.33 mm.
Is the Japanese size the same as the EU size?
No. EU sizes are the circumference in mm (for example 51), while the common Japanese scale uses small numbers (for example 11). A Japanese 11 is about EU 51.