In the adult Rule of Nines, what percentage does the anterior trunk (front torso) represent?

• A. 9%
• B. 18%
• C. 4.5%
• D. 27%

Answer: (B)

Understanding this is about how the Rule of Nines apportions burn size. In adults, the body is divided into large sections that each represent a fixed percentage of total body surface area to quickly estimate burns. The trunk is split into front and back, with the front (anterior trunk) accounting for 18% of total body surface area (the back, or posterior trunk, is another 18%). The head is 9%, each arm 9%, each leg 18%, and the genital area 1%.

So the anterior trunk represents 18% of body surface area, since the front of the torso makes up half of the trunk’s 36%. If both front and back of the trunk are burned, that would total 36%.