Join the Boob or Bust - Bra measuring advice Facebook page. Read all the useful information in the featured posts then use their very accurate calculator. I’m a size 12 and wear a 30 band. If you put a tape measure level all the way around you in the crease under your boobs and pull tight that is your under bust measurement. The Boob or bust calculator asks for 4 measurements including a leaning one. If your an A cup that means each breast protrudes from your under bust by 1/2”, does that sound right? Give the boob or bust calculator a go, it costs you nothing and you could end up with a better fitting bra, you’re probably not the size you think you are. There are 197k women, all ages, shapes and sizes and once you have your correct size someone will be able to recommend a tried and tested bra in your actual size. M&S try to put me in a 34DD, I’m actually a 30F and I’m not big. Good luck