When taking body measurements, you need to use the correct type of tape measure. You will want to use a soft cloth or flexible plastic tape measure, similar to what a seamstress uses. Do not use a metal measuring tape, used in construction (your measurements will be inaccurate).
Pay special attention not to pull your measuring tape too tight. Doing so will produce a measurement that is too small. The most difficult measurement is the bottom measurement. Too often, people measure too high along the bottom of their limbs producing a larger "Bottom" measurement. Ideally, measure 2 inches up from the bottom of your limb and use a pen to mark this level on your limb. Once you know exactly where to measure, use a tape measure to carefully measure your bottom circumference.