Body surface area (BSA) estimates the total area of your skin in square metres — about 1.9 m² for an average man and 1.6 m² for an average woman. The Mosteller formula computes it as the square root of height (cm) × weight (kg) ÷ 3600. Medicine uses BSA to dose chemotherapy and index cardiac output.
Body surface area — BSA — is the measurement medicine reaches for when body weight alone is not precise enough: chemotherapy doses, cardiac output indexing and burn assessment are all calculated per square metre of body surface. This BSA calculator uses the Mosteller formula, the version most hospitals use at the bedside, to estimate your body surface area from just height and weight.
Calculate your BSA below, then read on: the formulas, normal values, and why oncology and cardiology dose by surface area instead of weight.
Body Surface Area (BSA)
Mosteller formula, used in drug dosing and clinical calculations.
What is body surface area?
BSA is the estimated total area of your skin, expressed in square metres (m²). It matters because many physiological quantities — metabolic rate, cardiac output, kidney filtration — track body surface more closely than body weight. That is why your lab’s eGFR is normalized “per 1.73 m²” (the historical average adult BSA) and why a cardiologist reports cardiac index as output divided by BSA.
The BSA formula: Mosteller and Du Bois
Direct measurement being impractical, BSA is estimated from height and weight. The two classic equations:
- Mosteller (this calculator): BSA = √( height (cm) × weight (kg) ÷ 3600 ). Simple enough for mental arithmetic, and the most used in clinical practice.
- Du Bois (1916): BSA = 0.007184 × height(cm)0.725 × weight(kg)0.425. The historical standard many references were built on.
The formulas agree within a few percent for most adults — a difference that rarely changes clinical decisions but explains why two calculators can show slightly different numbers.
Normal BSA values
| Group | Typical BSA |
|---|---|
| Adult men (average) | ~1.9 m² |
| Adult women (average) | ~1.6 m² |
| The “standard adult” used in lab normalization | 1.73 m² |
| Children (about 10 years) | ~1.1 m² |
| Newborns | ~0.25 m² |
Why medicine doses by BSA
Chemotherapy is the flagship example: most cytotoxic drugs are prescribed in mg per m², because drug clearance correlates better with surface area than with weight, and the therapeutic window is narrow enough that the improvement matters. BSA also anchors cardiac index in cardiology, fluid resuscitation in burn medicine (together with burn-percentage charts) and several pediatric dosing conventions — although children’s medication is more often dosed per kilogram, as our pediatric dose calculator explains.
BSA vs BMI
They share inputs and nothing else. BMI (weight ÷ height²) classifies body composition risk; BSA estimates body size for physiological scaling. A BMI of 32 says “obese range”; a BSA of 2.1 m² just says “large person” — with no judgement attached. For health assessment, BMI, body fat percentage and waist-to-height ratio are the right tools; BSA is the dosing and indexing tool.
This tool is informational. Actual drug dosing by BSA is calculated and verified by the treating team — never dose any medication from an online calculator.
Frequently asked questions
What is a normal body surface area?
About 1.9 m² for adult men and 1.6 m² for adult women. The 1.73 m² you see on lab reports is a historical standardization value, not a target.
How is BSA calculated?
Most commonly with the Mosteller formula: the square root of height (cm) times weight (kg) divided by 3600. The older Du Bois equation gives near-identical results for most adults.
Why is chemotherapy dosed by body surface area?
Because the clearance of many cytotoxic drugs tracks body surface better than weight, and their narrow safety margins make that precision worthwhile. The care team calculates, caps and adjusts these doses individually.
What does per 1.73 m² mean on my kidney test?
Your eGFR is scaled to the surface area of a standard adult so results are comparable between people of different sizes — it is a normalization convention, not your personal measurement.
Is BSA affected by body fat?
Only through weight: the formulas cannot distinguish fat from muscle. Two people with the same height and weight get the same BSA regardless of composition — one reason some modern dosing moves toward lean-mass-based methods in specific drugs.
Numbers are a starting point — not a diagnosis
If your results raise questions, Acibadem specialists can review your situation properly: share your case and receive a free, no-obligation medical opinion from the relevant department.