so i finally got some bras, and i wish someone somewhere had just explained what the numbers and letters on bra sizes relate to, i would have grasped this so much faster. the number is the measurement for the band that fits around your ribcage just beneath your breasts. the letter is the size of the cup that supports your breasts. fit this to the universal uk sizes, combine the number and letter for your bra size, then use that or use the measurements to compare to whatever non-uk sizing guides are being used.
why they don't just lay this stuff out more clearly is beyond me, tbqh.