Your arms must be relaxed at your sides. Measure around the fullest part of your chest.
Measure around your ribcage, directly underneath the bust.
Measure around the narrowest part of your natural waist, generally around the belly button. To ensure a comfortable fit, keep one finger between the measuring tape and your body.
With your feet approximately 6" apart, measure around the fullest part of your hips. This area usually corresponds to the top of your legs.