Armhole: Circumference from shoulder tip to armpit.
Shoulder Across: Straight, horizontal measurement from shoulder tip to shoulder tip.
Bust: Circumference around the fullest part of your bust & straight across your back keeping the tape a litle loose for comfort. You don't need to take off your undergarment when you take this measurement.
Waist: Circumference of your natural waist, on top of your navel.