I weight 130 pounds, 5'7, and wear a size 6, so I ordered the medium adult size.  It made a ripping sound when I tried to put it on, and the waist was directly under my bra, and the bottom hem didn't even cover my butt.  This would fit about an 8-10 year old child, not even a small adult.  Also was very cheap, like something from the dollar store, with unfinished seams, threads hanging off everywhere, just looked like a wrinkled up plastic bag.  Pretty shockingly bad for the price I paid, so back it went.  I have seen the same quality KIDS costumes at the Dollar Tree for $1, and this was absolutely not even an adult small, much less medium.  Not sure why they are marketing a cheap childs costume as an adult costume.