You need to take the measures below twice. Once while you are wearing your most supportive bra and again while you are not wearing a bra. 1. Over Bust Measure your high chest under your armpits and around your back. Keep the tape measure parallel all the way around. Do not pull too tightly. 2. Bust Line Measure the circumference around the fullest point of the bust keeping the tape level. Do not pull too tightly. 3. Under Bust Measure the circumference under your bust keeping the tape measure parallel all the way around. 4. Width of Bust Measure the bust from the cleavage, through the apex (highest point of the breast), to near the underarm where the bust ends. Large or droppy breast should be measured while lying down. 5. Depth of Bust Measure the bust from the apex (nipple) down to the ribcage where the bust ends. Large or droppy breast should be measured while lying down.