Measure your bust circumference at its fullest point, wearing a bra without padding. Stand with feet hip-distance apart and find the widest part around your bust. Keep the measuring tape parallel to the ground and try not to pull the tape too tight – it should not indent the skin.

Measure the circumference under your bust, around the rib cage where the elastic band of a sports bra would land. Be sure you do not "flare" your rib cage or suck in your breath. Keep the measuring tape parallel to the ground and try not to pull the tape too tight – it should not indent the skin.