In the adult Rule of Nines, what percentage is assigned to the trunk (anterior)?

• A. 18%
• B. 13%
• C. 9%
• D. 21%

Answer: (A)

Understanding how the adult Rule of Nines estimates burn size hinges on how body regions map to percentages. The anterior trunk refers to the front of the torso—the chest and abdomen. In adults, this region is assigned 18% of total body surface area, with the back of the trunk also 18%, making the trunk total 36%. Other regions follow the familiar multiples of 9%: head and neck 9%, each arm 9%, and each leg 18%. So the front of the torso is 18% because it represents half of the trunk’s 36% allocation. The other options don’t fit this standard distribution: 9% corresponds to the head/neck or a single limb, 13% and 21% aren’t used in the Rule of Nines.