Japan Ring Size to US: A quick Guide
March 31, 2026
A simple guide to understanding Japanese and US ring sizes
Converting a Japan ring size to US may seem simple until you start comparing charts.
If you are drawn to Japanese jewellery, whether while travelling in Japan or ordering from a Japanese brand online, converting a Japan ring size to US may seem simple until you start comparing charts. Many brands, manufacturers, and online stores provide accurate sizing within their own system, but the problem often starts when they try to convert those sizes into other standards, if they offer conversions at all. Those references are often limited, simplified, or geared more towards their own catalogue than towards giving users a reliable comparison. If you already know your size in Japan or in the US, what you really need is a clear reference point.
How the Japanese and US ring size systems work
US ring size system
The US system is used in the United States, Canada, and quite often in Mexico. It is also one of the most common references in online jewelry retail. Sizes are based on the inner diameter of the ring in inches, and each full size increases in regular steps. It is one of the most widely used ring size systems internationally, especially in ecommerce.
Japanese ring size system
The Japanese system is based on JIS S 4700:2022 and uses the ring’s inner diameter in millimetres. It follows regular 0.33 mm increments, with sizes running from 1 to 35. This system is aligned with ISO 8653:2016 while adapting the standard to local practice, which is why it remains the official reference in Japan.
Japan ring size to US conversion
For a quick reference, the list below is based on the official conversion tables published by RingSize.Online. For more exact conversions, diameter-based checks, or comparisons with other systems such as UK, EU, Swiss, Brazilian, or Indian sizes, readers can also consult its official ring size conversion chart.
- Japan ring size 8 is equivalent to US size 4.5.
- Japan ring size 9 is equivalent to US size 5.
- Japan ring size 10 is equivalent to US size 5.5.
- Japan ring size 11 is equivalent to US size 6.
- Japan ring size 13 is equivalent to US size 6.5.
- Japan ring size 14 is equivalent to US size 7.
- Japan ring size 15 is equivalent to US size 7.5.
- Japan ring size 17 is equivalent to US size 8.
- Japan ring size 18 is equivalent to US size 9.
- Japan ring size 20 is equivalent to US size 9.5.
- Japan ring size 21 is equivalent to US size 10.
- Japan ring size 23 is equivalent to US size 10.5.
- Japan ring size 24 is equivalent to US size 11.
- Japan ring size 25 is equivalent to US size 11.5.
- Japan ring size 27 is equivalent to US size 12.5.
- Japan ring size 28 is equivalent to US size 13.
- Japan ring size 30 is equivalent to US size 13.5.
- Japan ring size 31 is equivalent to US size 14.
RingSize.Online's conversion tool lets users compare ring sizes across all major international standards, including diameter and circumference.
This is especially useful if you are comparing sizes from Japanese jewellery stores, marketplaces, or independent designers. Many beautiful rings are sold using local sizing only, so having a clear Japan to US reference helps you shop with more confidence and reduce the risk of ordering the wrong size.
Japanese jewellery brands worth exploring
If this conversion is part of a wider interest in Japanese jewellery, a few names are especially worth knowing. Mikimoto is probably the best known internationally, particularly for pearl jewellery, but it also offers ring collections. TASAKI is another strong reference, with a more contemporary luxury style built around pearls and diamonds. Ginza Tanaka is also well established, especially in gold and platinum jewellery. If you are browsing Japanese brands, having the size sorted first makes everything easier, especially when the ring you like is listed only in Japanese sizing.
Sources:
RingSize.Online PDF: https://ringsize.online/wp-content/uploads/Conversion-Ring-Size-Chart.pdf
JIS S 4700:2022 PDF
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