This should help www.wikihow.com/Take-Measurements-(For-Wom
" 1 - Strip down to your underwear and stand in front of a full-length mirror.
2 - While standing straight, bend over to the front or side and make a note of where your body creases. This is your natural waist. It should be the narrowest part of your waist, and it is generally located between your rib cage and belly button.
3 - Return to an upright position.
4 - Wrap the tape measure around your natural waist, keeping it parallel to the floor. Wrap the tape measure around your natural waist, keeping it parallel to the floor.
5 - Do not hold your breath or suck you stomach in.
6 - Stick your thumb beneath the tape measure to prevent yourself from drawing it too tight.
7- Bring the tape measure together in the center front of your body.
8 - Look at the number in the mirror or carefully look down at it while keeping your back straight.
9 - Mark the number down on paper."