Would someone who’s into bra intervention help my friend.

[TheLightSideOfTheMoon]

Band size: 42
Bust size: 51

Every calculator says something different and we’re both losing the will to live.

Thanks.

Using the method of deducting the band measurement from the bust measurement, I would make it out to be 42H

Maybe try the boob or bust website.

Start point would be a 42G - there's a DD and ff cup to consider and its 1 cup size per inch.

That said, it's not uncommon for women with larger back sizes to need a smaller band than they measure as a larger bra stretches more in absolute terms. So when she tries on she should be looking for a band which fits snugly, and that can only fit 2 fingers under it. If the 42 is big (which it might be) then try a 40 but with a GG or H cup.