When it comes to bra sizing, one area of international understanding is the system of cross grading. The essence of this system is that the complete front of the bra (side seam to side seam) is also used for three other sizes, for example the front section of 1 34B is also the front section of a 36A, 32C, and 30D. This system can be explored further in the area of the cup wires.
The buying public is in complete denial over this cross grading system; most believe the volume of a 34B cup is identical to that of a 36B or 38B cup, and that only the band/back size is changing.
If we consider a worst case scenario, a large brand offering band sizes 30 – 40” and cup sizes AA – A – B – C – DD – E – F – FF – G – GG – H – HH – J – K – L. That is 96 size options, multiply that by 3 colorways, (different dye colors affect fit) and you have 288 potential fit problems and stock options.
From research over the last 10 years it would seem that there are only 5 or 6 back sizes across the cup sizes to make up the following. For instance:
Excerpt from “Bra Sizing – The International Confusion” by David Morris, published in the November 2014 issue of the Intimate Apparel Journal.