Bought the black xs to go under the larkspur midi dress because they didn't bother lining the skirt portion (grrrrrrrrrrr).
my stats are 34a-28/29-36 and the xs fit very smoothly around the chest and was flowy around my lower half, so i would say it's running big.
the straps are very pretty and it could easily be nightwear too.
i'm 5'6" and it came to just below my knees.