I'm pretty skinny, weighing 145 at 5'11". I got the medium and it fits GREAT. It's decently snug with a little room, and the sleeves are a perfect length, just a little long. The only thing that's a little tough is that it's not incredibly flexible, so don't expect to do anything super active in it. If I put my arms straight forward the back is pretty tight, and if I put them straight up the whole coat comes with it. It's perfectly fine for normal wear, but any hard physical activity might do some damage. It's not terribly thick, but is great for cooler spring/summer nights. I was skeptical to buy something like this online, but I have no regrets.
I'm 5'9" 160 lbs athletic-type and this casual jacket is perfect! Great for Spring weather or a night out. I even spoke to a live assoc when choosing medium or small and they were on the $ with the medium. Really pleased with the purchase and the assistance.
it felt hollow and a bit cheap. The arms were super tight making it difficult to wear anything other than a tee...lame. Returned.