Measurements on the size charts are based on the measurements of your body, not the garment. To use the size chart find your measurements and match to the correct garment size.
Measure your waist at the narrowest point
Measure your hips at the widest point
Measure around your chest/bust while holding the measuring tape under your armpit
While standing measure from your crotch to the floor. If ordering a custom inseam you can either measure yourself or a pair of pants you own. For the pant measure from the crotch to the end of the leg.
Measure from the center of the back of your neck, along the length of your arm to your wrist while keeping your arm slightly bent