Body Surface Area (Mosteller)

BSA by Mosteller: body surface area

BSA (Body Surface Area) is the external area of the body, given in m². Clinicians use it to scale drug doses and physiologic indices across people of different sizes. The Mosteller formula from 1987 caught on more than any other because you can work it out at the bedside without a calculator: BSA (m²) = √((height_cm · weight_kg) / 3600). A typical adult lands around BSA ≈ 1.73 m², with children proportionally smaller. Alternative formulas include Du Bois (1916), the original; Boyd (1935), seen in some pediatric protocols; and Haycock (1978), also for children. Across normal body sizes Mosteller stays within roughly 3% of all three. Example: an adult 175 cm tall weighing 70 kg has BSA = √(175 · 70 / 3600) = √3.403 ≈ 1.84 m².

Clinical context

In oncology, BSA is the usual basis for dosing. Most chemotherapy is prescribed per m² (5-FU at 400 mg/m², doxorubicin at 60 mg/m²) because it tracks organ mass and blood volume more closely than weight by itself. The same logic shows up in pediatrics for cytotoxic and renal-adjusted drugs, in cardiology for the cardiac index (CO/BSA, normally 2.5–4 L/min/m²), and in burn assessment through the Wallace rule of nines for adults and the Lund–Browder chart for children, which accounts for the proportionally larger head in infants. Clinical research also leans on it to normalize results across mixed cohorts.

FAQ

Mosteller, Du Bois, or Haycock? In adult oncology Mosteller is the default in practice, and it's the easiest to compute. Du Bois has historically done a bit worse at the extremes of body size. Some pediatric protocols lean toward Haycock and Boyd. In most cases the gap between them stays under 3–5%.

Should BSA be capped in obese patients? Plenty of cytotoxic protocols cap BSA at 2.0 or 2.2 m² to avoid overdosing, on the grounds that adipose tissue doesn't add proportionally to drug clearance. ASCO 2012 guidance, on the other hand, recommends full BSA-based dosing in most cases. Defer to your local protocol.

What's a normal BSA range? Adult women average about 1.6 m² and adult men about 1.9 m². Newborns sit near 0.25 m², and a 10-year-old child around 1.1 m².

Is BSA the same as BMI? No. BMI (kg/m²) stands in for body composition, while BSA (m²) is an area used to scale doses. Two people with identical BMI can land far apart on BSA once height comes into play.