Between Sm and Med
I ordered both sizes just to be sure, but (and this has never happened to me before) neither fit. the small has perfect length (front and back) as well as the sleeves. In the shoulders/upper arms it feels a little tight but is so stretchy that I think even for extremely arm-movement intense sports like skate skiing it would be fine. But the trunk/middle area is snug (and I'm a slim build); if I needed to wear an extra layer or even a vest it's too tight. But the medium has a much larger ovarall fit, too long in sleeves/body and just looks like I'm swimming in it. Very disappointing because it seems like a very nice and functional jacket. Didn't take it outside to test in cold, but feels quite substantial and warm.