US ring size to Japanese ring size
Handy when buying from Japanese shops that list sizes as numbers like 9 or 13.
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How to use it
- Enter us size.
- The result appears straight away and updates as you edit.
- Copy the result, or copy a link that keeps the same values to share it.
How it is calculated
US diameter = 25.4 × (0.458 + 0.032 × size). Japanese size = (diameter − 13) × 3 + 1, rounded to a whole number.
Example
Inputs: US size = 7. Result: Japanese size: 14; Inner diameter: 17.32 mm; Inner circumference: 54.4 mm.
Limits and caveats
- Uses the JCS scale found in most Japanese shops; the JIS scale equals JCS + 40.
- Sizes are rounded to the nearest step of each system, and shop mandrels can differ slightly.
Questions about this tool
What is US 7 in Japanese sizes?
Its diameter is 17.32 mm, which is Japanese size 14.
How are Japanese sizes defined?
Size 1 has a 13 mm inner diameter and each size adds 1/3 mm.
Is the Chinese size the same?
Many Chinese shops use similar numbers but charts vary, so compare the diameter in mm.