If you are not sure which size to choose, we recommend that you take your measurements by following these simple steps: BRAS: Full Bust= Measure directly over the nipple area, keep the tape tight enough to keep it from sliding. Underbust = Measure snugly around the ribcage, directly under the bust. Snug but not too tight. UNDIES & OTHERS: Waist: Find the narrowest part of your waist, usually above your belly button and below your ribs. Hips: Measure around the fullest part of your pelvis, keeping the tape measure parallel to the floor.