Your Shoulders: This is the hardest measurement to do by yourself, so you really should ask someone to help. Place the measuring tape at the tip of one shoulder and wrap it all the way around you like a shawl until it meets back at the same shoulder. The tape should skim the top of your shoulders so closely, it almost slips off. This is the widest circumference of your shoulders.
Your Bust: Stand up straight and wrap the measuring tape around your back and across the fullest part of your breasts, usually the middle of them. Pull the measuring tape as taut as you can without changing the shape of your breasts. If things start to squish, you've gone too far.
Your Waist: Wrap the measuring tape around your torso, at the smallest part of your natural waist. It should wrap flat around your back without buckling and meet just above your belly button.
Your Hips: Hold the measuring tape at one hip, below your hip bone, at the fullest part of your hip. Then, keeping the tape flat, wrap it around the largest part of your butt (no cheating!), your other hip, and bring it back to the meeting point.
Now that you've measured yourself (shoulders, bust, waist and hips), use those numbers to help determine your silhouette shape.