AT08 Shirt Sizes? (as compared to USA)

[Zeke.]

I am looking to buy many things at AT08 when I attend the Osaka showing this weekend, but how do the sizes compare to USA sizes? I am planning on buying 2 AT08 shirts (one of each color). I usually wear a small here in the US but wouldn't that be just a little smaller over in Japan? What about sweatshirts/hoodies? I want to buy a hoodie as well so should I get a medium or large? What sizes are they available in - just S, M, L? Thanks everyone.