Body Surface Area (BSA) Calculator
Body surface area — the skin's total area in square meters — is how many medications, especially chemotherapy, are dosed. Compute yours with the Mosteller formula, cross-checked against Du Bois.
How to use this calculator
- Enter your height in centimeters and weight in kilograms.
- Press Calculate to get BSA by both standard formulas.
- The two methods agreeing closely (they usually do) indicates a robust estimate.
Formula used
Height in cm, weight in kg, BSA in m². Mosteller (1987) is the modern clinical favorite for its simplicity; Du Bois (1916) is the historical standard many references still cite. They typically agree within a few percent.
Example calculation
170 cm, 70 kg: Mosteller = √(11,900 ÷ 3,600) = √3.306 = 1.82 m²; Du Bois gives 1.81 m² — essentially identical.
Why medicine doses by surface area
Metabolic rate, cardiac output and drug clearance track body surface area better than raw weight — a 100 kg person doesn't process drugs at twice the rate of a 50 kg person. That's why chemotherapy doses read "mg per m²" and why cardiac index divides output by BSA.
No formula measures your actual skin; each is a regression fitted to measured bodies. Mosteller's elegant square root made bedside calculation practical and is now the default, but the choice of formula can shift a dose by a few percent — one reason clinical dosing always involves professional verification.
Why use this calculator?
- Understand the m² figure on medical documents and dosing references.
- Cross-check the two standard formulas in one calculation.
- Get context — how your BSA compares to the adult average.
Frequently asked questions
What is a normal BSA?
Adults average about 1.7 m² — typically ~1.6 for women and ~1.9 for men. A newborn is around 0.25 m². Your figure depends on both height and weight.
Why do different BSA calculators disagree slightly?
Several published formulas exist (Mosteller, Du Bois, Haycock, Gehan-George), each fitted to different historical datasets. Differences are usually 1–3%. Mosteller is today's common clinical default.
Is BSA used for anything besides drug dosing?
Yes — cardiac index (heart output per m²), burn assessment (the rule of nines describes % of BSA burned), and normalizing kidney function (eGFR is reported per 1.73 m², the historical "standard adult").