I'm an usually a small, which I bought, thought be great after baby, but fits fine now, 20wks, 5'5" 140lbs, 34C... usually 128lbs 34B, but I think this will fit me fine then,  could probably fit an xs too. Really cute style and waist is stretchy so works as maternity dress too. I'd say small is dress size 4-6. I'll update with a picture after I wash and fluff out wrinkles.