Arms relaxed at your sides, measure around the fullest part of your chest/bust (around shoulder blades and under arms). Do not pull tight; the measuring tape should be straight and flat against the body, yet comfortably loose.
Length
Stand up straight. Either use a mirror or have a friend measure from the top of the shoulder about an inch from the neck. Extend the measuring tape down along the body to the distance shown on your selected size. This will be the approximate position of the bottom edge of the garment.
Waist
Determine the position you want the waistline of your pants to rest when worn and measure around this portion of your body. The measuring tape should be straight and flat against the body, yet comfortably loose.
Inseam
Remove your shoes and stand up straight. Start the tape measure high in the crotch. Keep the tape straight, and measure down along the inside of your leg to the floor.