This body surface area calculator computes your BSA in square meters using both standard clinical formulas — Mosteller and Du Bois — the number medicine uses to dose chemotherapy, size burns care and index cardiac output.
Educational tool — clinical dosing decisions belong to clinicians using verified measurements. BSA in ft² is also shown in the explainer below (1 m² ≈ 10.764 ft²).
Why Medicine Measures Your Skin From the Outside
Many physiological quantities scale with surface area better than with weight: heat loss, metabolic rate, kidney filtration, cardiac output — and crucially, how the body handles many drugs. Dosing per square meter normalizes across a small child and a large adult in a way per-kilogram dosing cannot. The two standard formulas:
- Mosteller (1987): BSA = √(height × weight ÷ 3600) — designed to be memorable and calculator-friendly; the modern default in most hospitals.
- Du Bois (1916): BSA = 0.007184 × H^0.725 × W^0.425 — the century-old original, derived from painstaking measurements of nine subjects (including, famously, a cretin and a child — the formula’s small-sample origin is a beloved medical-history footnote).
Both live in our Health Calculators collection, alongside the weight-context tool everyone meets first, the BMI Calculator.
Worked Example (Verified)
175 cm, 70 kg:
- Mosteller: √(175 × 70 ÷ 3600) = √3.4028 = 1.84 m² (1.845, rounded)
- Du Bois: 1.85 m² — reassuring agreement (the formulas differ by ~1% for typical adults, more at extremes)
- In imperial: ≈ 19.9 ft² of skin — about the area of a standard door and a half
Where BSA Is Used
- Chemotherapy dosing: most cytotoxic drugs are prescribed in mg per m² — BSA errors translate directly into under- or over-dosing, which is why oncology double-checks height and weight on the day.
- Burns: burn size is expressed as % of total BSA (the “rule of nines” partitions the body into 9% blocks) to drive fluid resuscitation.
- Cardiac index: cardiac output ÷ BSA normalizes heart function across body sizes (normal ≈ 2.5–4.0 L/min/m²).
- Kidney function: eGFR results are standardized to a nominal 1.73 m² body — near the population average adult BSA.
- Average adult BSA: ≈ 1.7 m² (women) to 1.9 m² (men); a newborn is about 0.25 m² — a sevenfold range that per-kg dosing alone handles badly.
Related Tools
- BMI Calculator
- Lean Body Mass Calculator — the other body-composition measure
- Health Calculators — the full collection
Frequently Asked Questions
How is body surface area calculated?
Most commonly with Mosteller’s formula: BSA = √(height in cm × weight in kg ÷ 3600), in square meters. For 175 cm / 70 kg that gives 1.84 m².
Which BSA formula is more accurate?
They agree within ~1–2% for typical adults. Mosteller dominates modern practice for its simplicity; Du Bois remains the historical reference. Neither is a true measurement — direct methods (3D scanning) show both drift at body extremes.
What is a normal body surface area?
Adults average roughly 1.6–2.0 m² depending on height and weight (textbook “standard” ≈ 1.73 m²). Children range from ~0.25 m² (newborn) upward as they grow.
Why not just dose drugs by weight?
Because metabolic rate and organ function track surface area more closely than mass — a tall lean person and a short person at the same weight process many drugs differently. BSA dosing reduces (though does not eliminate) that mismatch.
Is BSA the same as BMI?
No. BMI = weight ÷ height² describes body composition (how heavy for your height). BSA estimates skin area for dosing and physiology. The calculator shows your BMI only as context.
Is this body surface area calculator free?
Yes — free, instant, no sign-up. Educational only; not for clinical dosing.