Using the rules of nines with an adult, the percentage of the total body surface area of the anterior trunk or posterior trunk is 18%. Rule of nines is a formula for estimating percentage of body surface areas, particularly helpful in judging the portion of skin that has been burned. For the adult, the head represents 9%; each upper extremity 9%; the back of the trunk 18%, and the front 18%; each lower extremity 18%; and the perineum the remaining 1%.
