Originally Posted by conradwu
Your observation is correct. I'm average build and have to size up 1 size. If you're white and lift then you need to size up 2 sizes.
If you are large by western standards in the shoulders and chest (irrespective of ethnicity), I wouldn't bother at all. The amount of tailoring involved would probably not be worth it and other measurements would be way off (particularly length, which is difficult to deal with in jackets).
IME, Japanese tailoring, like clothes sizing all over the world, varies quite a lot in its size assumptions, but they are certainly not compatible with western vanity sizing!
I'm short (5'5" / 165cm) but I have a real chest measurement of 37 and am not narrow in the shoulder. In western sizing, I am generally a British / US 36 (European 46, or 'Small'), although old-fashioned 37S is often the best. 38/48/Medium is always too big. In Japan, I've tried things on that were labeled as a 38/48/M that were like a western 34/44/XS in the shoulders, but on the other hand, I've also tried other brands that were perfect for me, particularly those that claim to be imitating an 'English' cut: the jacket of the Avon House 3-piece tweed I bought recently was labelled as S, and looks like it was cut just for me. I imagine for most Japanese guys, the shoulders would be rather large.
If you're buying a suit, it is very likely that you will have to buy separates (if available) as RTW suits that come as is are likely to be way too narrow in the hips and seat). I generally take an M size trouser in Japan if the jacket size is S, but sometimes I have to take an L. In general, it's probably more trouble than it's worth trying to buy trousers in Japan if you're of average western dimensions!
The other thing is that many Japanese brands use a 0,1,2,3, etc. scale, where 0 is usually between 32/42/XXS - 34/44/XS and so on, plus they will generally use metric measurements, except in MTM / bespoke tailoring.
In short, if you are an average-proportioned westerner*, and are going to buy Japanese clothing:
1. read the full sizing information very carefully;
2. be totally honest about your own measurements;
3. preferably try things on in person - I'd be very wary of buying any Japanese clothes over the Internet if you don't know the brand's sizing assumptions and have never tried them on before - and,
4. however nice the stuff looks - and IME, ordinary Japanese clothes are generally of a much higher standard than ordinary western clothes - be prepared to search for longer than you are used to for something that really fits you.
*If you an average proportioned American, I'd probably give up now.