Japanese Clothing, Shoe, and Bedding Sizes: A Conversion Guide

A "M" arrives from a Japanese online store and it's snug through the shoulders in a way your usual M never is. That's not a fluke or a mislabeled item. Japan runs its own sizing systems for clothing, shoes, and even bedding, built around different reference bodies and different units than the ones most incoming residents grew up with. This guide walks through all three, with conversion tables you can use for a rough match, and it's honest about where the sources behind those tables don't fully agree.

Clothing: two systems running at once

Japanese women's clothing carries two labels that often appear on the same tag. The letter system (S, M, L, LL, and sometimes 3L) reads like the sizing you already know, but it isn't calibrated to the same body. The 号数 (gō) number system is older and more precise, tied to a specific bust measurement under the Japanese Industrial Standards (JIS): 9号 is the reference size at roughly an 83 cm bust, with each two-号 step adding about 3 cm. Retailers commonly print both, and the rough correspondence most Japanese size guides give is 7号=S, 9号=M, 11号=L, and 13号=LL.

Treat that overseas column as a starting point only. A frequently repeated rule of thumb is that Japanese sizing runs about one size smaller than US or UK sizing for the same numeric bust, and cuts are often shorter in the torso and narrower in the shoulder even at a matching bust figure. Some Japanese brands now sell in S/M/L only, with no 号 number printed at all, which makes the letter-to-号 table above a fallback for reading older size charts rather than something every label still uses.

Men's sizing is comparatively simpler, running mostly on S/M/L/LL/3L tied to chest circumference, though the exact centimeter range for each letter still varies by brand enough that a chart from one manufacturer won't reliably carry over to another's.

Shoes: sizing you can measure yourself

Japanese shoe sizing skips letters and arbitrary numbers entirely. The size printed on the box is your foot length in centimeters, so a 24.5 fits a 24.5 cm foot regardless of brand, at least in theory — width is a separate letter code (D, E, EE, EEE, 4E) that Japanese lasts tend to run narrow on, and that's usually the actual reason an import or a Japanese size that should fit doesn't.

Mainstream retail in Japan generally covers about 21.5 to 30 cm for women's shoes and about 23.5 to 30.5 cm for men's, though any single store's actual shelf stock is usually a narrower slice of that. Feet outside this range, especially on the larger end, often mean checking a specialty large-size retailer rather than a standard shoe shop.

Those US figures come from a widely repeated shortcut — roughly cm minus 17 for women's US sizing and cm minus 18 for men's, with UK landing around cm minus 19. It's a useful approximation, not a manufacturer standard, and different size-converter sites round it slightly differently. A half-centimeter difference at the boundary between two sizes can flip which whole US number you land on, so use the table to narrow your search, then check the actual insole length the retailer publishes for that specific model.

Bedding: names that describe width, not a fixed product

Japanese bedding and bed frames use their own naming set — シングル (single), セミダブル (semi-double), ダブル (double), and further up, クイーン (queen) and キング (king) — and every one of these names refers to mattress width only. セミダブル is the one with no real equivalent outside Japan: it sits between a Western twin and a full, and it's a common choice in Japanese apartments precisely because it's wider than a single without needing a full double-sized room.

The width figures above are fairly consistent across the manufacturer and retailer pages checked for this guide. Length is where it gets messier: a bed frame and mattress set is usually built to 195 cm, matching the Japanese bedding industry's standard, while a traditional futon sold separately is sometimes listed closer to 210 cm long. Neither number is wrong; they're describing different products that happen to share the same width name. If you're buying a fitted sheet, a duvet cover, or a mattress topper, match it to the exact centimeter dimensions on that specific listing rather than assuming "single" means the same length everywhere.

This distinction matters if you're furnishing an apartment through Mercari or Jimoty rather than buying new — our guide to buying secondhand furniture in Japan covers those platforms, and a secondhand bed frame or futon listed as "セミダブル" is exactly the kind of item where confirming the actual centimeters with the seller avoids an unpleasant surprise on pickup day. The same applies if you're weighing a rental subscription instead of buying outright: our comparison of CLAS, airRoom, subsclife, and MUJI's furniture rental terms is worth reading before you commit to a bed size sight unseen.

A short routine for buying without guessing

None of the tables above are precise enough to skip this step. The habit that actually prevents a wrong-size order is the same one regardless of category.

What this guide doesn't cover

This is a general reference for reading Japanese size labels, not a guarantee that any specific brand, store, or listing follows the figures above exactly. It doesn't recommend a specific retailer, and it isn't a fit or styling recommendation for your body. Kids' sizing, which runs on its own age- and height-based system separate from adult 号数, is also outside the scope of this guide.

Sources

The demand and topic basis for this guide came from four sources named in the byline above: FROM JAPAN BLOG, Interac Network (two articles, on clothing and on shoes), Japan Living Life, and Japan Living Guide. Direct fetches of blog.fromjapan.co.jp, interacnetwork.com, japanlivinglife.com, and japanlivingguide.com were blocked by this environment's network egress policy, along with every other domain checked below, so none of the figures in this article come from reading those pages directly. Instead, every number above was checked against search-engine result summaries of multiple independent pages, and cross-checked wherever more than one source was available. Two places where sources genuinely disagreed are called out directly in the body rather than resolved by picking one: the exact centimeter width of a シングル mattress (97 cm vs. 100 cm depending on the source), and the exact length distinction between a bed-frame mattress and a standalone futon (195 cm vs. 210 cm). The letter-to-号 clothing mapping and the cm-to-US shoe formula are both described consistently across sources as rough approximations, not fixed standards, which is how they're presented here.

• FROM JAPAN BLOG — Japanese clothing and shoe sizing guide: blog.fromjapan.co.jp
• Interac Network — clothes shopping in Japan: interacnetwork.com
• Interac Network — buying shoes in Japan: interacnetwork.com
• Japan Living Life — Japanese clothing sizes conversion: japanlivinglife.com
• Japan Living Guide — large-size shoes in Japan: japanlivingguide.com
• Kaken Test Center — JIS adult women's size reference table (号数/bust/hip): kaken.or.jp
• Japan Textile and Apparel Industry Federation (JWCA) — how women's clothing sizes are labeled: jwca.or.jp
• Nihonbashi-Nishikawa — semi-double mattress size explained: nihonbashi-nishikawa.com
• Nihonbashi-Nishikawa — full bedding/mattress size chart: nihonbashi-nishikawa.com
• OneMall — Japanese shoe size to US conversion chart: blog.onemall.jp