You will need to take measurements using a measuring tape.
When measuring the bust, the tape should fit closely to the body: across the fullest part at the front, through the underarms at the sides, and around the shoulder blades at the back.
The waist should be measured strictly horizontally at the narrowest part of the torso, passing through the most prominent point of the abdomen.
When measuring the hips, the tape should remain horizontal, passing around the middle of the thigh and across the fullest part of the buttocks at the back.