NWCA Medical Assistant Practice Exam

Estimating body surface area from height and weight uses the Mosteller formula, which gives BSA in square meters as the square root of the product of height in centimeters and weight in kilograms divided by 3600. This compact form is widely used in clinical practice because it provides a consistent, quick estimate from two easy measurements.

Why this form works well: height and weight relate to surface area, and taking the square root of their product scales the result to an area measure in square meters. The division by 3600 ensures the units line up so the final value is in m^2. For example, someone who is 170 cm tall and weighs 70 kg would have BSA ≈ sqrt((170×70)/3600) ≈ sqrt(11900/3600) ≈ sqrt(3.3056) ≈ 1.82 m^2, which matches typical adult BSA values.

Other forms shown would not yield the correct units or magnitude. Omitting the square root would give a quantity that scales linearly with height and weight rather than with surface area. Using a different divisor or not placing the division inside the square root would also misalign units and produce incorrect BSA values.