My usual fit is a 28F, I bought a small.  The band size fits perfectly, but the cups are too small (as expected)and don't have much stretch.  However it is very comfortable and supportive,and I can squeeze in for casual days- just expect a bit of muffin top and more cleavage than you'd really want on an average day.  Wanted to review because it's a solid design and I'm hoping they'll do more of a range of cup sizes in future.