BSA Calculator Guide: Body Surface Area Explained
Body Surface Area is a critical measurement in clinical medicine for drug dosing. Learn what it is, how it is calculated, and why it matters.
What Is Body Surface Area?
Body Surface Area (BSA) is the total surface area of the human body, measured in square meters (m²). Unlike weight or BMI, BSA accounts for both height and weight to estimate total body size.
BSA is used extensively in clinical medicine because many physiological processes — including cardiac output, drug metabolism, and heat exchange — scale with body surface area rather than body weight alone.
Average Adult BSA Values
- Adult female: ~1.6 m²
- Adult male: ~1.9 m²
- Average adult: ~1.7–1.8 m²
- Newborn: ~0.25 m²
BSA Formulas
Several validated formulas exist for calculating BSA. The choice depends on population and clinical context:
Mosteller (1987) — Most widely used
BSA = √(Height(cm) × Weight(kg) / 3600)
Simple and accurate. Standard in oncology.
DuBois & DuBois (1916) — Historical standard
BSA = 0.007184 × Height(cm)^0.725 × Weight(kg)^0.425
Widely validated but slightly underestimates BSA in obese patients.
Haycock (1978) — Preferred for children
BSA = 0.024265 × Height(cm)^0.3964 × Weight(kg)^0.5378
Most accurate for pediatric populations.
Gehan & George (1970)
BSA = 0.0235 × Height(cm)^0.42246 × Weight(kg)^0.51456
Better for very heavy patients.
Our BSA calculator supports all major formulas so you can compare results across methods.
Clinical Uses of BSA
BSA is an essential measurement across multiple clinical specialties:
Many cancer drugs are dosed in mg/m² to normalize for body size and minimize toxicity.
Cardiac output indexed to BSA (CI = CO/BSA) to compare heart function across differently sized patients.
eGFR is adjusted to 1.73 m² BSA to allow comparison across body sizes.
The "rule of nines" estimates body surface area burned to guide fluid replacement therapy.
Weight-based dosing in children is often supplemented with BSA calculations for chemotherapy and some antibiotics.
Some antibiotics are dosed per BSA to optimize effectiveness while avoiding nephrotoxicity.
BSA vs BMI
BSA and BMI both use height and weight, but serve completely different purposes in medicine and health assessment:
| Metric | BSA | BMI |
|---|---|---|
| Primary use | Drug dosing, cardiac indexing | Health/obesity screening |
| Unit | m² (area) | kg/m² (ratio) |
| Accounts for body size | Yes | Partially |
| Muscle vs fat | No | No |
| Who uses it | Clinicians, oncologists | Patients, public health |
FAQ
What is body surface area used for?
What is a normal BSA?
Which BSA formula is most accurate?
Is BSA the same as BMI?
Do I need to know my BSA?
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The ToolsACE Team
ToolsACE is an independent platform founded in 2023 by a team of software developers and educators. We build free, privacy-first tools and write guides to help people make better decisions — without sign-ups, paywalls, or data tracking.
