Body Surface Area (BSA) is one of the few human measurements that bridges geometry and physiology.
About this calculator
Body Surface Area (BSA) is one of the few human measurements that bridges geometry and physiology. Unlike weight or height alone, BSA correlates strongly with metabolic rate, blood volume, glomerular filtration rate and several drug clearance pathways. This makes it the gold standard for dosing chemotherapy, immunosuppressants like cyclosporine, certain cardiac drugs and many paediatric medications where weight-based dosing alone is inaccurate.
The five formulas in this calculator come from over a century of careful measurement and validation. The original DuBois & DuBois formula (1916) was developed from coating volunteers in plaster and then measuring the dried sheets. Modern formulas like Mosteller (1987) are easier to compute and validated against direct measurement and 3D body scanning. For most adults of typical body composition, all formulas agree within 5%. Differences become larger at the extremes -- very tall, very short, very obese or very underweight bodies -- where the underlying assumption that body proportions scale predictably breaks down.
The Mosteller formula is the most widely used in clinical practice today because of its arithmetic simplicity (a single square root) and good accuracy across age groups. Haycock is preferred in neonates and infants where the DuBois assumptions don't hold. Boyd's formula is sometimes preferred for very obese patients. This calculator runs all of them so a clinician can cross-check, but actual prescribing should always use the formula specified in the protocol or hospital pharmacy guideline. For dietary planning use the [[bmr]] calculator (which itself often uses BSA as an input) and the [[macro]] calculator; for body composition use the [[bmi]] and [[ideal-body-weight]] calculators.
Common uses
- Calculating chemotherapy or immunosuppressant doses (mg/m²)
- Cardiac index and ejection fraction calculations indexed to BSA
- Paediatric medication dosing where weight alone is insufficient
- Burn injury assessment combined with rule of nines coverage estimate
- Research and sports physiology where metabolic indexing is needed
Frequently asked questions
Which formula should I use?
Mosteller is the default for adults because it
Is BSA the same as body fat percentage?
No -- BSA measures the external skin surface area derived from height and weight; body fat percentage measures the proportion of mass that is adipose tissue. Two people with the same BSA can have very different body fat percentages.
Why do oncology protocols cap BSA at 2.0 or 2.2 m²?
Many chemotherapy regimens were developed in trials that excluded very large patients, so safe dosing data above 2.0-2.2 m² is limited. Capping reduces the risk of severe toxicity. The cap varies by drug and protocol.
Does BSA change rapidly?
BSA changes slowly, in proportion to height and weight. Major weight changes (5+ kg) shift BSA by 0.05-0.1 m²; height changes only matter in growing children. Re-measure BSA at significant weight changes for ongoing chemotherapy.
How accurate is BSA for predicting drug doses?
BSA dosing reduces dose variability compared to flat dosing or weight-based dosing for many drugs, but it is still an approximation. Modern oncology is moving toward pharmacogenomic and therapeutic drug monitoring to refine dosing further. BSA remains the practical standard.