I'm not sure of the exact measurements, but I can say I bought an XL, I'm 6'1", 170lbs and the arms and chest are more than large enough for me to fit 2 bulky layers of down, a thin fleece, and a thin base layer underneath with out feeling like it's making the sleeves too short or tight in the chest and back. This jacket is a great layering piece, I've only used it as a winter shell so far and I've put it through down pours and blizzard conditions both with amazing results. Do not expect an athletic fit as the cut is rather billowy, the pictures make it look much more form fitting than it is( which is not at all). In closing, the mountain hardwear ampato is generously cut all the way around so if you're just using it as a light rain jacket and you're around my size you'd be better off with a medium. Hope this helps.