F, 5'6", 168lbs, wear a size 14 bottom usually. Ordered a L and it fit like a glove! I'm super hippy (pear-shaped) and these are the only shorts that don't ride up terribly when I'm walking. They're very stretchy but retain their shape well, even when wet (I've worn them while kayaking and they didn't stretch-out while I was sitting for hours and hopping in and out of the water).