I need this for a trip to Europe where the late spring weather can be changeable, so it needed to be big enough that I could wear layers underneath.  I first bought the Large but it was a little small through the shoulders and arms to comfortably fit a sweater underneath.  I ordered the Extra Large and it is plenty roomy.  The rest of the coat is a roomy swing style that should fit many sizes and shapes, but as other reviewers have noted the arms are a bit narrow. I will be keeping both as they are in different colors.  FYI I am 5'3" and usually wear a medium.  The XL comes just above my knee and, of course the sleeves need to be rolled up.