I wear XS or S in most items. Knowing that swimsuits tend to run small, I got a medium. Oh man, it was way too small still and I felt a little crushed in it. I think it's hard in general to buy suits that aren't separates as not everyone has the same butt/hip to boob ratio - and I think this may have been part of the problem. I returned but didn't love it enough to exchange for a bigger size.