When measuring your chest to find the best band size, Nordstrom's top bra fitter Sandra Saffle says to make sure the measuring tape is secured low and snug on the back. Most women secure their bra band too high on the back, causing the band to ride up and the cup to fall forward. Also, make sure to lift the breast tissue up when measuring—that way the tape is snug on the rib cage.
If your bra band lies across your shoulder blades, you've got it all wrong, Sandra says. The band should fit around the smallest part of your back.