What is body surface area (BSA)?
Body surface area is an estimate of the total outside area of the human body, expressed in square meters (m²). It is commonly used in medicine to scale drug dosing, estimate metabolic needs, and support certain clinical decisions. Unlike a simple weight-based measurement, BSA takes both height and weight into account.
In practice, BSA is not measured directly in routine care. Instead, it is estimated through formulas derived from population studies. Because of that, you may see slight variation in values depending on the formula selected.
Why clinicians use BSA
Body surface area is widely used in healthcare contexts such as:
- Chemotherapy dosing: Many oncology protocols calculate doses by m².
- Pediatric medicine: Medication amounts are sometimes scaled to body size more precisely than weight alone.
- Kidney and cardiac evaluation: Some lab or imaging results may be indexed to BSA.
- Burn assessment and fluid planning: Surface-area concepts are central in trauma and critical care.
While useful, BSA should always be interpreted in context. Age, organ function, body composition, and diagnosis still matter for real-world decision-making.
Formulas included in this calculator
1) Mosteller formula
Mosteller is one of the most popular methods because it is simple and performs well in many adult settings:
BSA = √((height in cm × weight in kg) / 3600)
2) Du Bois & Du Bois formula
A classic historical formula that remains widely referenced:
BSA = 0.007184 × height0.725 × weight0.425
3) Haycock formula
Frequently considered in pediatric contexts:
BSA = 0.024265 × height0.3964 × weight0.5378
4) Gehan-George formula
Another validated method with slightly different exponents:
BSA = 0.0235 × height0.42246 × weight0.51456
5) Boyd formula
The Boyd equation adjusts for body mass scaling in a more complex way:
BSA = 0.0003207 × height0.3 × (weight in grams)(0.7285 − 0.0188 × log10(weight in grams))
How to use this body surface calculator
- Select your units (metric or imperial).
- Enter weight and height.
- Pick one formula or choose “Show all formulas.”
- Click Calculate BSA to get your value in m².
If you use imperial values, the calculator converts pounds to kilograms and inches to centimeters before running the formulas.
BSA vs BMI: what is the difference?
BSA and BMI are often confused, but they answer different questions:
- BSA (m²): Estimates external body area and is commonly used for dosing and indexing.
- BMI (kg/m²): Relates weight to height and is used mainly for broad weight-status screening.
One is not a replacement for the other. They are tools built for different tasks.
Limitations you should know
No BSA formula is perfect for every population. Values can vary by age, ethnicity, body composition, edema status, and clinical condition. In obesity, frailty, or extreme body size, protocols may require adjusted body weight, capped dosing, or specialist interpretation.
This calculator is intended for educational use and quick estimation. For medication dosing, diagnosis, or treatment, always follow professional medical guidance.
Quick FAQ
What is a typical adult BSA?
Many adults fall roughly between 1.5 and 2.2 m², but healthy values can be outside that range depending on body size.
Which formula is best?
There is no universally “best” formula for every case. Mosteller is common for simplicity, while institutions may use specific formulas based on their standards.
Can I use this for children?
The calculator can estimate pediatric BSA, but pediatric dosing must follow pediatric-specific references and clinician oversight.