I wear large in the SG Grumman & every other shirt/ coat / jacket from everyone else. When I looked into this jacket there were a lot of comments on the SG site that said it was a lot bigger than their regular sizes. I called SG & a guy said it was designed to be an outside layer so if I was only gonna wear one layer like a merino long sleeve then I should definitely get the medium. (for reference I'm 6-0" & 170 lbs). It's an athletic fit so if you're close to my size & you're gonna wear it over multiple layers then it may be too small but it fit me fine over 1 shirt. I used it as work/ dress shirt.
