If you wear bras, you’ve likely got a few in your drawer that you avoid because their fit is a flub. Or maybe you’ve resigned to wear them anyway, even though they pinch or squish your precious parts.

“I’m about a handful, I think I’m a D cup. My sister’s way bigger, she’s probably a G.” We’ve all heard banter like this with people throwing around their best guesses for bra size. In the words of ...