Measure under your arms at the fuller part of your bust. Keep tape level across your shoulder blades.
Measure around your natural waistline, keeping the tape comfortably loose.
Measure around your body 1 1/2" below your natural waist.
Stand with your feet together and measure around the fullest part of your hips.
Using a pair of your pants that fit well, measure from crotch seam to bottom of leg.
Wrap a length of string around your finger and mark where the end touches. Measure the distance between the end of the string and the mark you've made to determine what size to order.