Body Surface Area (BSA) Calculator
Estimate body surface area quickly using common clinical formulas. Choose your units, enter height and weight, then click calculate.
This tool is for education and planning. For medication dosing or treatment decisions, use clinical judgment and local protocols.
What is BSA?
BSA stands for Body Surface Area, a measurement of the total external area of the human body. It is usually expressed in square meters (m²). In medicine, BSA can be useful for estimating drug doses, fluid needs, and physiologic parameters that scale better with surface area than with body weight alone.
Why a BSA calculator is useful
A BSA calculator helps convert height and weight into a practical estimate clinicians can use at the bedside or in planning. Common use cases include:
- Medication dosing for selected therapies that are prescribed by m².
- Burn assessment support in conjunction with burn area charts and clinical protocols.
- Renal and cardiac indexing when normalizing physiologic values to body size.
- Pediatric and adult comparison where body size differences matter.
Formulas included in this calculator
Several BSA equations exist. They produce similar but not identical results. This page includes four commonly referenced options:
| Formula | Equation (height in cm, weight in kg) | Notes |
|---|---|---|
| Mosteller | BSA = √((height × weight) / 3600) | Simple and widely used in routine clinical practice. |
| Du Bois & Du Bois | BSA = 0.007184 × height0.725 × weight0.425 | Historic formula based on early anthropometric work. |
| Haycock | BSA = 0.024265 × height0.3964 × weight0.5378 | Often referenced in pediatric contexts. |
| Gehan & George | BSA = 0.0235 × height0.42246 × weight0.51456 | Derived from broader body-size data than some older equations. |
How to use this BSA calculator correctly
1) Choose units first
Select metric or imperial units before entering values. If you use imperial inputs, the calculator converts them to centimeters and kilograms automatically.
2) Enter accurate height and weight
Small input errors can slightly shift the final result. Use measured values whenever possible.
3) Select the formula your workflow requires
If no specific formula is mandated, Mosteller is a common default due to simplicity and broad acceptance.
4) Interpret in context
BSA is one data point, not a complete clinical picture. Always combine it with age, comorbidities, labs, and professional judgment.
BSA vs BMI: not the same thing
People often confuse BSA with BMI (Body Mass Index). They answer different questions:
- BSA estimates external body area and is mainly used for scaling physiology and dosing.
- BMI screens for weight status categories at the population level.
In short: BSA is a size-scaling tool, while BMI is a weight-status screening tool.
Typical adult BSA range
Many adults fall roughly between 1.5 and 2.2 m², but normal varies with body size, sex, age, and population. The most important factor is consistency: use the formula required by your clinic, protocol, or study design.
Frequently asked questions
Is one formula always best?
Not universally. Different institutions standardize different equations. The “best” formula is usually the one aligned with your clinical protocol.
Can I use this for children?
The tool can calculate pediatric BSA, but pediatric dosing must follow specialist references and child-specific safety checks.
Why does BSA change if I switch formulas?
Each formula was derived from different datasets and mathematical fits. Differences are usually modest, but can matter in dose-sensitive settings.
Bottom line
A BSA calculator is a practical way to transform height and weight into a clinically useful measurement. Use it carefully, choose the correct formula for your setting, and always pair numeric output with sound medical judgment.