To choose the correct size for you, measure your body as follows:
Measure under your arms, around the fullest part of your chest. Measure under your arms, not around them.
Measure around your natural waistline - this is usually the narrowest point on your waist with one finger between your body and the measuring tape
Stand with your heels together. Measure around the fullest part of your hips. The tape should sit level across the middle of your backside.