Measurements refer to body size, not garment dimensions.
HOW TO MEASURE YOURSELF
Your measurements will be most accurate if someone else measures you. Make sure your feet are directly under your shoulders, and let your arms hang down by your sides (see photo for reference).
Measure the circumference at the fullest part of your chest and across your shoulder blades.
Measure the circumference of your waist at your natural waistline. If you bend to the side, the crease that forms is your natural waistline.
Measure the circumference of your hips over your hip bones and around the fullest part of your buttocks.