I currently have a XS, S, and M in my possession. I have had trouble finding a size that fits. I also have two other MHW jackets, both smalls (one fits well and one is too big) and a MHW small vest which is WAY too big. Not sure what the deal is. I'm 5'6" and 115 lbs. As for this jacket: The XS was too small all around, and especially tight in the arm pits. The small fits pretty well, but only has room for a base layer underneath. However, it too is very tight in the arm pits and the sleeves are just a tad too short to have my thumbs in the holes while my arms are bent in a running pose. My upper body is not bulky by any measure. As a last resort I bought the medium and it is WAY too big. About three inches wider than the small and the sleeves are about 1-1.5 inches longer. I would suggest going with the medium or ordering a couple of sizes and sending back what doesn't fit. Good luck!

I'm typically a size 10-12 with average length torso and slightly longer arms. I got size L, and it fits perfectly with room for a non-bulky fleece or wool underneath.

This jacket is the perfect cold weather running jacket. So it is designed to fit snug- tight so that it does not flop around when running. I cannot fit much under it other than a thin long sleeve shirt. The arms, as mentioned previously, are long. There is a thumb hole for added warmth so the sleeves are meant to sit longer than usual. This works well for me because most tops that fit me have arms that are too short.

I ordered a L and it was too big and boxy and then ordered a M and it fit everywhere except it was too short in the torso. Not the best fit for long bodies...

tends to run small..