According to the Rules of Nines, what does 4.5% represent?

• A. 4.5% - half of the front upper/lower extremity / front and back of the head
• B. 9%
• C. 18%
• D. 1%

Answer: (B)

In burn assessment using the Rule of Nines, body surface area is divided into large regions with fixed percentages. The head and neck region is 9% of total body surface area. That 9% is treated as two equal halves: the front of the head and the back of the head. Each half represents 4.5% of total body surface area, so 4.5% corresponds to half of the head’s surface (either the front or the back). This is not half of a limb or a trunk region. Other regions have their own full percentages: the entire head and neck is 9%, each leg is 18%, the anterior trunk is 18%, the posterior trunk is 18%, each arm is 9%, and the groin is 1%.