I am 5'5, 148lbs, athletic build, I wear a size 34B bra size, and generally size 6 pants, (semi big booty), I ordered a medium and it fits perfectly. The bottoms don't give me any appeance of a muffin top, the top is comfortable. If I didn't have a drawer full of bathing suits, (or my BF wouldn't see the packages arrive in the mail), I would order another suit.