As other reviewers have stated, this does tend to run much smaller that your normal size. I normally wear between a 0-4 or XS-S, depending on the brand. I am 5'8", 115 lbs, with a 34A-B chest. I ordered the Medium, just to be on the safe side. It went on with no problem & fit quite well... if my chest was a LITTLE larger(or the top a LITTLE smaller), it would have been perfect, but it had a tendency to bunch up, as it wasn't skin-tight. All in all, it was a good buy & it served it's purpose. Just ensure you order a size or 2 larger than you normally would in order for it to fit.