The problem with Bra sizes are numerous. The top "measurers" do it by eye. No 2 women are the same, in terms of, the taper, in the rib cage and the ratio between width & depth of the rib cage; so any chart is only a starting point. The vast majority of British women, wear bras, with too big a band & too small a cup, from using standard measuring charts.
To this we have to take account of the fact that genetic males have a, more or less parallel rib cage, while women's taper. Add to this the fact that bras, allegedly of the same cup size, can vary quite dramaticaly and we have a quagmire! Also remember, the bulk of breast tissue, for any given cup size, increase dramaticaly, as band size increases.
As a T girl, who wears bras full time, I offer 2 main pieces of advice. Take your underbust measurement as the starting point; you may vary 2 inches either way, but it is a good starting point. Asess your cup size and ere towards the small size for band & cup.
Try an underwired bra. The line, left by the underwire, should perfectly encompasse your boob. The under wire, should lie on your chest wall. If you are a band size too small, you will know instantly. If you are a size too big, the ends of the wires will tend to chafe your skin, below your armpit.
The cup should have no, or very minimal creasing and please do not commit the cardinal sin of spilling out of your bra.
Now let the fun begin.
