Please keep in mind that the bust measurement is tricky on my blouses because the pleating allows each size fits a wide variety of wearers. For example, the armpit-to-armpit measurement on the medium expands from 18 inches lying flat to 22 inches when the pleats are expanded. This means it can accommodate a bust circumference from 36 to 44 inches. It's going to look best on someone with a bra size of 40 or less, however, as you wouldn't want the pleats fully expanded for aesthetic reasons. As a reference, I have a bust circumference of 39 and am usually a L or XL in most blouses. I wear a medium in my own Spirit Dress products, however, because I wear a B cup bra and don't need the extra space in the large to accommodate my bust.