Never assume you "know your size" when shopping in another country like Japan. If you do, you are sure to find yourself either buying something that doesn't fit or googling size comparison charts to figure our what a 10 and a half size shoe is in centimeters. Trust me, I must have stood in the shoe store for a ridiculously long time trying to search for American to Japanese size conversions. I`m sure I looked like a lost child, or maybe they thought I was playing Pokemon Go, i`m not sure really. Either way it was embarrassing enough. But fear not, you don`t have to resort to online shopping to avoid these situations.
It`s one of those being more culturally sensitive or culturally open minded things. Realizing that things don't work the same here as they did back home. Rules, laws, and more can be very different. Like measuring temperature in Celsius versus Fahrenheit, or using the Metric system versus the Imperial system. After three years living in Japan, I still have to convert temperatures in the forecast from Celsius to Fahrenheit.
Japan has some of the greatest fashion in the world and there are countless stores all across the country for you to check out. The staff are usually amazing and very helpful in helping you get the right things, but don't usually speak English. Whether on vacation, shopping for fun or out of necessity you will, and should, find yourself doing some clothes shopping in Japan.
American vs Japanese Sizes
General rule of Thumb
Always assume that the sizes marked are off by one or more. For example, assume a small (s) is actually an extra small (xs), a medium (m) is actually a small (s), a large (L) is actually a medium (m), and so on.
Japanese size American size
LLL (3L) XL
I have come across shirts marked as a LL that fit like an American medium size as well. So of course try on everything. If, you can't try it on, then air on the side of caution. For example, All the teachers at the school I teach at will always order a shirt to wear during the schools sports festival. Unfortunately, there is no way to try them on first and it was too difficult to make sense of the size guides in the catalogue. To be safe I assumed a Large would probably fit like a medium, so I ordered an extra large. Luckily, I was still able to squeeze into the shirt and not look ridiculous. It turned out that the extra large fit me like a medium size in the US. Needless to say that for my second sports festival, I ordered a size bigger.
Asking for help, even with limited Japanese ability can go a long way. Translators and apps make it much better, but here are some useful phrases to help make it even easier.
試着してもいいですか？ - May I try this on? / (literally) Try on, is it ok?
Shichyaku shite mo iidesuka
試着室はどこですか？ - Where are the dressing rooms?
Shichyaku shitsu wa dokodesuka
鏡はどこですか？ - Where is a mirror?
Kagami wa dokodesuka
Really, most of the things you might need can be as simple as learning a few words and combining them with the grammar ~はどこですか. Simply put you are just asking where ~ is.
English Japanese Kana Kanji
Changing room Shichyaku Shitsu しちゃくしつ 試着室
Mirror Kagami かがみ 鏡
Restroom Otearai / Toire おてあらい お手洗い
Clothing store Yōfuku-ya ようふくや 洋服屋
Shoe store kutsu-ya くつや 靴屋
Liquor store Saka-ya さかや 酒屋
For example if you just need to see something in a mirror, you would ask were is a mirror by combining kagami 鏡 (the Japanese word for mirror) with wa doko desu ka (~はどこですか？).
Kagami wa doko desu ka?
Where is a mirror?
Sometimes you will get lucky and find shoes that are marked with both American and Japanese sizes, but not always. I learned my general size in centimeters and went from there. Here are some general size comparisons to get you started.
American size Japan size in cm
10 1/2 28*
* Yes, I realize sizes 10 and 10 1/2 are both marked as 28 cm, but that's just how it works in Japanese shoe sizes. It`s a closest approximation in some cases
American size Japan size in cm
** See above annotation for men's shoe size.
Conclusions and other options
In the end, all I can really do is give you a rough approximation of where to start when it comes to shopping for your size in Japan. Trying it on is still the best way to go of course. However I have recently found out about a new service being used in Japan by a company called Zozo. This service allows you to request a body suit through the app, the zozosuit, that you use to take a picture of yourself while wearing. The app then uses the image to obtain precise measurements of your body and uses those measurements to make sure you get the right size every time. This service is especially helpful for people like me who struggle in finding the right size and have no fashion sense.
Also, be sure to check out the second hand stores across Japan. Most Japanese people take great care of their things. This means you can find some amazing deals on fantastic things in these stores. They are sometimes referred to as recycle shops. One of the bigger ones I have seen is a chain called Second Street. I found some great and stylish boots for the winter there and they were super cheap. Unlike back in the U.S., second hand stores in Japan will often have many of the latest fashion trends too. Check it out and hope this helps next time you get lost shopping in Japan.