Many online bra dealers include directions for measuring yourself for a bra-- though that's no guarantee you'll get your best size. For American sizes, it's typically to measure around your chest under your breast area, then add 5 to that number. The first time I did it I came up with 34, so I ordered a 34A from Victoria's Secrets. It was too small. The next bra I bought was a 36A and the band was about right. It did require pads or forms to fill out the cups, though. I didn't have any extra flab on my chest, so even an AA cup left the cups empty. I did buy a couple of bralettes that fit me fairly well without any insert. A bralette is a sort of simpler version of a bra, without underwiring and usually made of stretchy material.