I found a chart a plastic surgeon developed to determine cup size. It's based on a 36 band size. This has been the only chart that I have used which has given an accurate idea of what bra size might fit - for example, I'm currently between 7.5-8", which is a 36A or B, the sister size of which is 32C or 32D.
7.5/19.1 Full A
8.5/21.6 Full B
9.5/24.1 Full C
10.5/26.7 Full D
The idea is that you measure each breast individually, from where the tissue starts near your armpit, across the nipple to the breast bone.
This is the link, but there's no chart there, just a detailed explanation on how he came up with this method: http://www.plasticsurgerypractice.com/20...ra-sizing/