If your measurements are not consistent with a single column, use your waist measurement to determine your ideal size.
Bust
Measure around the fullest part of your chest, keeping the tape level to the floor
Underbust
Measure directly under your bust (around your rib cage, where your bra band sits), keeping the tap
Waist
Measure around your natural waistline (the smallest part of your waist).
Hips
Measure aroud the fullest part of your hips. Slim-hipped ladies can take this measurement from 20cm/8in below the waistline.