Body Surface Area (BSA) Calculator
Calculate Body Surface Area using the Mosteller formula.
Supports metric and imperial units.
Used for medication dosing and clinical assessments.
Body Surface Area (BSA) is the total exposed surface area of the human body measured in square meters (m²). Unlike body weight alone, BSA accounts for both height and weight, making it a more accurate predictor of metabolic function — which is why it is used extensively in medical dosing calculations.
Mosteller Formula (most widely used in clinical practice):
Metric:
BSA (m²) = √[(Height cm × Weight kg) / 3600]
Imperial:
BSA (m²) = √[(Height in × Weight lbs) / 3131]
Other validated BSA formulas:
| Formula | Equation (Metric) | Notes |
|---|---|---|
| Mosteller (1987) | √[(Ht × Wt) / 3600] | Simple; most commonly used |
| Du Bois & Du Bois (1916) | 0.007184 × Ht^0.725 × Wt^0.425 | Original formula; widely published |
| Haycock (1978) | 0.024265 × Ht^0.3964 × Wt^0.5378 | Best accuracy for children |
| Boyd (1935) | 0.0003207 × Ht^0.3 × Wt^(0.7285 − 0.0188×log(Wt)) | Complex; rarely used clinically |
All four formulas agree within 2–3% for adults of average build. Differences become more significant in obese patients or very small children.
Reference BSA values by population:
| Population | Average BSA |
|---|---|
| Newborn (3.5 kg) | 0.23 m² |
| 1-year-old | 0.47 m² |
| Child (10 years) | 1.14 m² |
| Adolescent (16 years) | 1.60 m² |
| Adult female | 1.60–1.70 m² |
| Adult male | 1.85–1.95 m² |
Worked example: Adult male: Height 180 cm, Weight 80 kg BSA (Mosteller) = √[(180 × 80) / 3600] = √[14400 / 3600] = √4.0 = 2.00 m²
Clinical applications of BSA:
- Chemotherapy dosing: Most cytotoxic drugs are dosed in mg/m² to normalize across body sizes and reduce toxicity risk
- Burn assessment: The Rule of Nines estimates percentage of BSA burned to guide fluid resuscitation (e.g., each arm = 9%, each leg = 18%, torso front = 18%)
- Cardiac index: Cardiac output (L/min) ÷ BSA → normalizes heart function across different body sizes
- Drug clearance: Renal function (GFR) is often reported as mL/min/1.73 m² (normalized to a reference BSA of 1.73 m²)
- Pediatric dosing: Children’s doses are often BSA-based rather than weight-based for precision
Important note: BSA is a geometric approximation. Individual anatomy, age, sex, and ethnicity can influence the accuracy of any formula.
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