Here's a pic of the blue one in a 54.
I'm usually a 23" chest /18.5-19" shoulder in most everything. I would say the jacket is pretty generous when buttoned from the chest to the waist. i've worn a hooded zip up sweat shirt under it with no issues buttoning the jacket with pulling or tightness.
It's on the shorter side, my only real issue (if any) is the pocket holes sit up pretty high.