Here are some tips to help you order the correct size. If you don't have a measuring tape, use a piece of string and hold it alongside a ruler.
Lift your arms slightly and measure around your body, crossing over the fullest part of your chest.
Place your hand on your hip with your arm bent at 90 degrees. Measure from the middle of the back of your neck, across the shoulder, and down your arm to the wrist.
Measure around your waistline at the level where you normally wear your pants. Keep a finger between your body and the measuring tape for an accurate fit. For low-rise pants, measure a little bit lower than your natural waist.
Stand with your heels together and measure around the fullest part of your hips.