BSA Calculator (Body Surface Area)
Calculate body surface area (BSA) using multiple formulas (Mosteller, Du Bois, Haycock, Gehan & George, Boyd) with metric or imperial units. Includes pediatric and veterinary (dog/cat) options.
This tool is for educational purposes only and does not replace clinical judgment. Always verify doses and calculations in accordance with your local protocols.
What is body surface area (BSA)?
Body surface area (BSA) is an estimate of the total external surface of the human (or animal) body, expressed in square meters (m²). It is widely used in medicine to:
- Normalize drug doses (e.g., chemotherapy, some antibiotics, immunosuppressants).
- Index physiological measurements (e.g., cardiac output, GFR, lung function).
- Estimate metabolic rate and fluid requirements.
Most commonly used BSA formulas
All formulas below use height in centimeters (cm) and weight in kilograms (kg) after unit conversion.
\[ \text{BSA}_{\text{Mosteller}} = \sqrt{\frac{\text{height (cm)} \times \text{weight (kg)}}{3600}} \]
\[ \text{BSA}_{\text{Du Bois}} = 0.007184 \times \text{height (cm)}^{0.725} \times \text{weight (kg)}^{0.425} \]
\[ \text{BSA}_{\text{Haycock}} = 0.024265 \times \text{height (cm)}^{0.3964} \times \text{weight (kg)}^{0.5378} \]
\[ \text{BSA}_{\text{Gehan}} = 0.0235 \times \text{height (cm)}^{0.42246} \times \text{weight (kg)}^{0.51456} \]
First compute: \[ W = \text{weight (kg)}, \quad \log_{10}(W) \] Then: \[ \text{BSA}_{\text{Boyd}} = 0.0003207 \times \text{height (cm)}^{0.3} \times \left(1000 \times W\right)^{0.7285 - 0.0188 \times \log_{10}(W)} \]
Pediatric weight-based formula (Mosteller variant)
For quick pediatric estimates when height is not available, a simplified weight-based formula is sometimes used:
Veterinary BSA formulas (dogs and cats)
Veterinary oncology and internal medicine often use species-specific BSA formulas:
\[ \text{BSA}_{\text{dog}} = 0.101 \times \text{weight (kg)}^{2/3} \] Cat
\[ \text{BSA}_{\text{cat}} = 0.1 \times \text{weight (kg)}^{2/3} \] Other small animals (generic)
\[ \text{BSA}_{\text{generic}} \approx 0.1 \times \text{weight (kg)}^{2/3} \]
Typical BSA values
| Population | Approx. BSA (m²) |
|---|---|
| Adult female (160 cm, 60 kg) | ~1.6 m² |
| Adult male (175 cm, 75 kg) | ~1.9 m² |
| Child 5 years (~18 kg, 110 cm) | ~0.75 m² |
| Newborn (~3.5 kg, 50 cm) | ~0.23 m² |
| Dog 20 kg | ~0.8 m² |
| Cat 4 kg | ~0.25 m² |
How to use this BSA calculator
- Select the appropriate mode: adult/child, pediatric (weight-only), or veterinary.
- Choose metric or imperial units. The calculator automatically converts to cm and kg internally.
- Enter height and weight (or weight only for pediatric/vet modes).
- Optionally enable the dose helper and enter a dose per m² to get the total dose.
- Click Calculate BSA to see BSA from all supported formulas.
Which BSA formula should I use?
There is no single universally “correct” formula. In practice:
- Mosteller is widely used because it is simple and performs well across a broad range of body sizes.
- Du Bois is the historical reference and still used in many clinical studies.
- Haycock and Gehan & George are often preferred in pediatrics.
- Boyd may be more accurate in very small or very large patients.
- For veterinary patients, species-specific formulas are recommended.
Always follow your institution’s protocol or the dosing recommendations from the specific drug monograph.
Limitations and safety notes
- BSA is an estimate and should not be the only factor guiding therapy.
- In obesity, underweight, or edema, consider whether to use actual, ideal, or adjusted body weight as per guidelines.
- For high-risk drugs (e.g., chemotherapy), double-check all calculations and use independent verification.
- This calculator does not store or transmit personal health information.