Chest is measured 1" below armhole. Body length from highest point of shoulder. Shoulder width from seam to seam.
NOTE: If measurements seem wrong, they may be of the item laid flat. For instance, a waist measurement may NOT be the distance all around your waist - it could be kind of just across the front of your waist. Some manufacturers give measurements for taut fabric (longer numbers) and some give them for slack or relaxed (shorter numbers).