How do I measure properly?

With the tips you measure correctly:

Your Chest Circumference:
Place the tape measure horizontally under the armpits and over the strongest part of your chest.

Your Waist Circumference:
You measure your waist circumference at the level of your natural waist. That is, between the highest point of your hip bone and your lowest rib arch.

Your Hip Circumference:
Put the tape measure around your hips. Measure the circumference at the strongest point of the buttocks.