Why Clinicians Care About Skin Area
Many drugs distribute through body water and tissue mass, which scale better with surface area than with weight alone. That's why cytotoxic chemotherapy doses are prescribed in mg per m² of BSA.
BSA also normalizes physiological measurements across body sizes: cardiac output as cardiac index (L/min/m²) and GFR per 1.73 m² are both BSA-indexed.
The Formulas Compared
Mosteller: √(H×W/3600), simple, accurate enough, and the modern default. DuBois & DuBois (1916) is the historical standard that defined the field. Haycock improves fit for children; Gehan-George was validated on a broader sample.
In practice the formulas agree within a few percent for average adults. What matters clinically is using one formula consistently when tracking a patient.
What BSA Does Not Mean
BSA isn't a health score, there's no healthy range to hit. It's an input to other calculations, like a tape measure is to a tailor.
Extremes of height or weight stretch the formulas' accuracy, which is why oncology protocols include dose caps and body-weight checks.
Sources
FAQ
What is normal body surface area?
Most adults measure between 1.6 and 2.0 m², depending on height and weight.
Which BSA formula do doctors use?
Mosteller is the modern standard for its simplicity; Haycock is often preferred in pediatrics.
Why is chemotherapy dosed by BSA?
Many cytotoxic drugs distribute through metabolically active tissue, which scales with surface area better than weight alone.
Important disclaimer: Results are educational estimates, not a substitute for professional medical advice. Discuss your numbers with a clinician before acting on them.