Measure around the fullest part of your bust, under the arms, over the bottom of your shoulder blades and across the apex of your chest. Do not pull the tape measure too hard, it should be secure but not taut against the body.
Measure around the narrowest part of your waist — typically one inch above the belly button.
Measure around the fullest part of your hips — typically 8" below your waist. Keep your feet together for the most accurate measurement.