Ring Size Conversion for Japan and East Asia
How the Japanese numeric ring scale works, how it maps to US, UK and EU sizes, and what to check when buying from Asian retailers.
5 min read
Japan uses its own numeric ring scale, also used widely in China, Hong Kong, Taiwan and South Korea. It runs from about 1 to 27 for adults and does not correspond to millimetres directly.
How the scale works
Japanese size 1 is roughly a 13 mm inside diameter, and each step adds about 0.26 mm of diameter, or roughly 0.8 mm of circumference. Because the steps are smaller than a US size, Japanese numbers climb faster: a US 7 is a Japanese 14, while a US 10 is a Japanese 20.
Useful reference points:
- JP 7 ≈ US 4 ≈ UK H ≈ EU 47
- JP 11 ≈ US 6 ≈ UK L½ ≈ EU 52
- JP 14 ≈ US 7 ≈ UK N½ ≈ EU 54
- JP 17 ≈ US 8½ ≈ UK Q½ ≈ EU 58
- JP 20 ≈ US 10 ≈ UK T½ ≈ EU 62
Why buyers get caught out
A Japanese 9 and a US 9 differ by more than three US sizes. Ordering a "size 9" from a Japanese retailer without checking the system is one of the most common international sizing mistakes. Always confirm which scale a listing uses; reputable Japanese sellers publish the inside diameter in millimetres alongside the code.
Chinese and Hong Kong sizing
Mainland China commonly uses the Japanese scale or the inside circumference in millimetres. Hong Kong uses a separate numeric scale that runs from about 1 to 27 but is not identical to the Japanese one. Where a listing is ambiguous, the millimetre figure is the only safe reference.
Korean sizing
South Korea generally follows the Japanese numbering, occasionally with a "ho" suffix. Treat a Korean listing as Japanese sizing unless the seller states otherwise.
Practical checklist for ordering
- Ask for the inside diameter in millimetres, not the code.
- Confirm the band width, since Asian fashion rings are often narrow and fit differently from a wide Western band.
- Check whether the ring can be resized; many plated fashion rings cannot.
- Allow for customs and returns, which can make an exchange impractical.
Enter your known size into the converter, read off the Japanese equivalent and the millimetre diameter, and quote the millimetre figure to the seller. That single step removes almost all risk from buying rings internationally.