Use your exact measurements when selecting your size.
Keep the tape firm, but not tight.
Measure over your undergarments not over existing bulky clothes.
Ask someone to help measure you.
Measure your height with no shoes.
Place your fist on your hip with your elbow forming a right angle. Measure from the bony prominence at the tip of your shoulder (acromion) to your elbow and then to the bony prominence at your wrist (where your cuff would sit).
The maximal circumference around your chest (with the tape measure remaining horizontal passing over your shoulder blades at the back, under the armpits and across your chest).
This measurement is taken around the smallest part of your waistline found between the top of the hip bones (iliac crests) and the lower ribs.