I got a medium large for my husband because he has broad, muscular shoulders and wears a size large shirt, though the rest of him is quite trim.  He loves the robe - it's cozy and warm but it is also huge!  He needs to roll up the sleeves three times otherwise they hang below his hands.  The robe is also longer than most - it comes down nearly to his ankles (he's about 70 in. tall).  On the other hand it keeps his legs warm so he doesn't need to wear it with long pants to be comfortable watching TV, etc.  If I ever need to replace this robe (he tends to wear things until they literally disintegrate) I'll probably look for the same brand but get a small/medium.