What's your underbust measurement and bust measurement at nipples?
Usually to work out bra size you take the underbust +4 inches to give the band size, then cup size is bust - band, e.g. I was 28 under and about 32 over, which gives 28+4=32 inch band size and if the band and bust measurement are the same that's an A cup (Bust 1inch bigger = B, 2inches bigger = C etc, bust inch smaller = AA, 2inches smaller = AA etc). Now I'm about 26.5 under and 33.25 over which works out at 30C but even 30D is a bit small so these things are not always accurate! Most calculation webistes are way off though, I've been told I'm 30E, 32A, 32B, 34AA ..... 32C or 30DD or 34B fit best.