For the most accurate results, measure yourself in your undergarments.
Measure size around the fullest part of your chest, keeping tape firmly under your armpits and around your shoulder blades.
Measure around your waist, slightly below your natural waist, where you normally wear your pants. Insert your forefinger between the tape and your body to allow ease in fit.
If your measurements are in between those listed in the size chart, pick the next larger size.