I've done a search and found lots of threads, but couldn't find one more recent. Apologies if this should be somewhere else.
I've just used the intervention method to measure. I'm a size 22 and measure:
41" under bust (40" pulled very tight, 42" comfortable) and 55" at the widest bent to 90 degrees.
Am I right that this makes me either a 40JJ or a 42 J? Marks and spencer put me in a 44F but it rides up at the back and the 42G I have the straps slip off at the shoulders all the bloody time. Constantly feel like my boobs are around my waist which makes me look much fatter than I am.