@canthugallcats: OK well I just measured myself and according to that chart, I should be around a G cup (my band size is 26.5, my overbust measurement is 35), or UK F cup. This would be accurate assuming that a 28 inch band fitted.
I wear either a 32DD or 30E (UK size; US equivalent would be 32DD/E or 30DDD/F), which is right, as I go by fit (I ensure that the band fit securely/snugly on the loosest setting, to allow for give, and to make sure that the band is providing the support, not the straps; I make sure the cups fit well, offering good coverage without gaping or creating bulges; I make sure there are no underarm or back bulges going on; and I make sure that the straps are comfortable and not the part of the bar providing support; I also make sure it sits below my shoulder blades at the back, and that the front sits flush, etc). Although my underbust measurement is pretty tiny, I find that in some shops, a 30 band measurement is too small, and so have to go down a cup size, and up a band size, and wear a 32DD. In others, it’s more accurate, so I take a 30E. But, a 28 would be way too tight; I’ve tied one, and can’t do them up lol.
I do agree that the majority of women wear the wrong sizes. I also think that in general, women don’t understand sizes. My friends look at me like I’ve got 2 heads when I tell them I wear a DD/E, because they think DD/E = huge. It doesn’t. Now, if I wear a 38DD/E, yes, I would have very large breasts; but because my band size is so small, they don’t look big, it just means they are big in comparison to my frame.
Most of my friends are wearing 1-2 band sizes too big, and 1-2 cup sizes too small (evidenced by that fact that their bras sit way too high up their backs, and the cups squish their breasts; ie it’s actually NOTICEABLE that they’re wearing the wrong size)), simply because they can’t/won’t accept they might be, say, a 30D, and not a 34B. What they don’t get is that the actual cup size for both sizes is basically identical, it’s just that the 30D has a smaller band, so will fit better. Drives me insane lol.