I've done a couple of different online calculators and gotten different results from all of them. I came across a few old threads on how to measure properly so thought I'd give it a go.
My band is just under 29" and when bending over my bust is between 38 and 39", but is 37" when stood up.
Currently wearing an M&S 32G. One cup is too small and the straps fall down despite being as tight as they'll go.