What percentage burn does a patient have who has suffered burns to one leg (circumferential), one arm (circumferential), and the anterior trunka. 18%
A general idea of the burn size can be made by using the rule of nines. Each upper extremity accounts for 9% of the total body surface area (TBSA), each lower extremity accounts for 18%, the anterior and posterior trunk each accounts for 18%, the head and neck account for 9%, and the perineum accounts for 1%. Although the rule of nines is reasonably accurate for adults, a number of more precise charts have been developed that are particularly helpful in assessing pediatric burns. Most emergency rooms have such a chart. A diagram of the burn can be drawn on the chart, and more precise calculations of the burn size made from the accompanying TBSA estimates given.
Children younger than 4 years have much larger heads and smaller thighs in proportion to total body size than do adults. In infants the head accounts for nearly 20% of the TBSA; a child's body proportions do not fully reach adult percentages until adolescence. Even when using precise diagrams, interobserver variation may vary by as much as ±20%. An observer's experience with burned patients, rather than educational level, appears to be the best predictor of the accuracy of burn size estimation. For smaller burns, an accurate assessment of size can be made by using the patient's palmar hand surface, including the digits, which amounts for approximately 1% of TBSA.