What is body surface area (BSA)?
Body surface area (BSA) is an estimate of the total external surface of the human body, usually expressed in square meters (m²). In medicine, BSA is often used when a value needs to be scaled to body size more precisely than body weight alone.
A BSA calculation can help with medication dosing, assessing physiological measurements, and standardizing values such as cardiac index or glomerular filtration rates. Because it combines height and weight, it often provides a more balanced body-size estimate than BMI for certain clinical tasks.
How this calculator works
This calculator lets you choose your unit system and one of several established BSA equations. Enter your measurements, click Calculate BSA, and the tool returns your estimated body surface area in:
- Square meters (m²) — standard medical unit
- Square feet (ft²) — additional reference unit
If you use imperial inputs (feet, inches, pounds), the values are converted internally to centimeters and kilograms before calculation.
BSA formulas included
1) Mosteller
BSA = √((height(cm) × weight(kg)) / 3600)
Simple, quick, and widely used in day-to-day clinical settings.
2) Du Bois & Du Bois
BSA = 0.007184 × height(cm)0.725 × weight(kg)0.425
One of the oldest BSA formulas, still commonly referenced in literature.
3) Haycock
BSA = 0.024265 × height(cm)0.3964 × weight(kg)0.5378
Often discussed for pediatric and mixed-age applications.
4) Gehan & George
BSA = 0.0235 × height(cm)0.42246 × weight(kg)0.51456
Developed from larger datasets than some older equations.
5) Boyd
BSA = 0.0003207 × height(cm)0.3 × weight(g)(0.7285 - 0.0188 × log10(weight(g)))
Includes a weight-dependent exponent and can produce slightly different estimates at extremes.
Common uses of body surface area
- Chemotherapy dosing: Many oncology regimens use mg/m² rather than mg/kg.
- Cardiology: Cardiac output may be normalized to BSA to produce cardiac index.
- Nephrology: Kidney function values may be normalized to 1.73 m² for comparison.
- Burn care: Estimating burn percentage and fluid needs often references body surface concepts.
Interpreting your result
Most adults fall roughly between 1.4 and 2.2 m², though normal values vary by age, sex, body composition, and population. A calculated BSA is an estimate—not a direct measurement—and different formulas can produce slightly different outputs.
In practice, clinicians usually stay consistent with one formula within a protocol to maintain comparability.
Limitations and practical notes
- All formulas are approximations derived from population data.
- Results may differ in very lean, very muscular, or severely obese individuals.
- Pediatric use may require age-specific clinical judgment.
- BSA should never replace full medical assessment.
Quick FAQ
Is BSA the same as BMI?
No. BMI is a weight-for-height index (kg/m²) mainly used for weight classification, while BSA estimates external body area (m²) and is often used for dosing or physiologic indexing.
Which formula should I choose?
Mosteller is a practical default. If your clinic or research protocol specifies another equation, use that one consistently.
Can I use this for medical decisions?
Use it for education and quick estimates. For treatment decisions—especially medication dosing—always follow professional guidance and institution-specific protocols.