To choose the correct size for you, measure your body as follows. Chest: Measure around the fullest part, place the tape close under the arms and make sure the tape is flat across the back. How To Measure Your Chest? Lift your arms and measure around the highest part of your chest and shoulder blades. Body: Measure the length of the front body from the middle point of the shoulder in between of the neck and armhole to the bottom of the rib.