In practice very few of the leading Australian manufacturers produce sizes F+ and many disseminate sizing misinformation. Breasts change shape quite consistently on a month-to-month basis, but they will individually change their volume by a different amount .

If the underwires poke the breast under the armpit or if the bra's center panel does not lie flat against the sternum, [35] the cup size is too small. The breasts should be enclosed by the cups and there should be a smooth line where the fabric at the top of the cup ends. The bust size, bust line measure, or over-bust measure is the measurement around the torso over the fullest part of the breasts, with the crest of the breast halfway between the elbow and shoulder, [64] usually over the nipples, [65] ideally while standing straight with arms to the side and wearing a properly fitted bra, [55] because this practice assumes the current bra fits correctly. It introduced a system with ten cup sizes per band size that are numbered and not lettered, designated as 1–36, 2–36 etc.Each cup's underwire at the front should lie flat against the sternum (not the breast), along the inframammary fold, and should not dig into the chest or the breasts, rub or poke out at the front.

There are lots of different styles, and each style has a dozen different sizes, and within that there are a lot of colors. If breast tissue overflows the bottom of the bra, under the armpit, or over the top edge of the bra cup, the cup size is too small.According to Tyrer, "to get the most supportive and fitted bra it's infinitely better if you know the volume of the breast and the size of the back.