I have a medium, and I'm normally a small mans size. It fits perfectly, just enough room to move. The small would have been too tight on me.
I wear Golite Reed pants, which ride high, so they go under the jacket fine.
I prefer a short jacket, rather than something than protects your upper thighs- which also constricts your movements to some degree when climbing or pushing up a steep hill.
I use it more an more in lieu of a windshirt, and I combine it with an ID Silcoat Cape, which acts like a pack cover too, and performs better on warm showery days in the Pyrenees.
Great jacket- mine's yellow in case I get lost.