BSA Formula Calculator
Calculate body surface area quickly using established formulas such as Mosteller, Du Bois, Haycock, Gehan and George, and Boyd. This tool helps you compare methods and understand how height and weight affect BSA in square meters.
Enter patient measurements
Results
Enter height and weight, choose a formula, then click Calculate BSA to view the estimated body surface area and compare formula outputs.
- BSA is commonly expressed in square meters (m²).
- Mosteller is widely used because it is simple and clinically practical.
- Different formulas may produce slightly different results, especially at body size extremes.
What is a BSA formula calculator?
A BSA formula calculator estimates body surface area, usually reported in square meters. In medicine, BSA is used as a practical way to scale certain physiological and treatment decisions to body size. While body weight alone is useful for many assessments, weight does not always describe body size as completely as a combined height and weight measurement. That is why body surface area formulas remain common in oncology dosing, burn assessment, fluid calculations, and selected reference ranges in clinical practice.
This calculator lets you estimate BSA from patient height and weight using several recognized equations. The output is not intended to replace professional judgment, but it provides a fast, structured estimate that can be useful in both academic and practical settings. In many hospitals, the Mosteller equation is favored because it is easy to use and closely tracks more complex formulas across a wide range of adults. However, alternative equations such as Du Bois, Haycock, Gehan and George, and Boyd can be relevant depending on institution, age group, or research setting.
Why body surface area matters in healthcare
Body surface area is often discussed because it acts as a size-normalizing metric. It is not perfect, and it should never be treated as the sole determinant of treatment. Still, BSA can be clinically useful because it includes both height and weight, which together may represent body dimensions better than weight alone in some scenarios.
- Chemotherapy dosing: Many anticancer drugs are traditionally prescribed in mg/m².
- Burn care: Burn extent is commonly described as a percentage of total body surface area, and fluid needs may depend partly on BSA concepts.
- Pediatric assessment: Some pediatric medication and physiologic reference values use BSA to help adjust for body size.
- Cardiology and nephrology: Certain physiologic measurements, such as cardiac index and glomerular filtration rate reporting conventions, may reference body surface area concepts.
The key point is that BSA is a measurement estimate, not a direct observation. It comes from formulas developed from body measurements in specific populations. As a result, every formula has limitations, and clinicians may prefer one method over another depending on the patient population and context.
The most common BSA formulas explained
1. Mosteller formula
The Mosteller equation is one of the most widely used because it is simple:
BSA = sqrt((height in cm × weight in kg) / 3600)
This formula is popular in everyday clinical workflows because it is easy to memorize and calculate. Despite its simplicity, it gives results that are generally close to more complex equations for many adults.
2. Du Bois and Du Bois formula
This is one of the oldest and most historically influential formulas:
BSA = 0.007184 × height(cm)0.725 × weight(kg)0.425
It remains a classic reference point in medical literature. However, because it was derived from a small original sample, some clinicians prefer later formulas in modern settings.
3. Haycock formula
The Haycock equation is often considered especially useful across a broader age range, including pediatric use:
BSA = 0.024265 × height(cm)0.3964 × weight(kg)0.5378
It is frequently cited when a more nuanced estimate is desired, particularly where child and infant calculations may be relevant.
4. Gehan and George formula
This formula is another validated alternative:
BSA = 0.0235 × height(cm)0.42246 × weight(kg)0.51456
It tends to produce results similar to other modern formulas, although minor differences may be noticeable in some patient sizes.
5. Boyd formula
The Boyd equation is more complex because it includes a logarithmic weight adjustment:
BSA = 0.0003207 × height(cm)0.3 × weight(g)(0.7285 – 0.0188 × log10(weight in g))
Because it uses body weight in grams and a logarithmic correction, it is less convenient for quick manual calculation but still important in historical and comparative discussions.
Comparison table: estimated BSA from common formulas
The table below shows how close formula outputs often are for a typical adult. Example patient: height 170 cm, weight 70 kg.
| Formula | Estimated BSA for 170 cm / 70 kg | Practical notes |
|---|---|---|
| Mosteller | 1.818 m² | Very common in clinical settings due to simplicity and speed. |
| Du Bois and Du Bois | 1.810 m² | Historically important and still widely referenced in textbooks and publications. |
| Haycock | 1.826 m² | Often used when broad applicability, including pediatrics, is desired. |
| Gehan and George | 1.833 m² | Produces a value close to other modern formulas in many adults. |
| Boyd | 1.835 m² | More mathematically complex; sometimes used for comparison or research context. |
How to use this BSA formula calculator correctly
- Enter the patient height in either centimeters or inches.
- Enter the patient weight in either kilograms or pounds.
- Select the formula you want to use as the primary displayed result.
- Click the calculate button.
- Review the main BSA estimate and compare it with the values produced by the other formulas.
The calculator converts units automatically before running the formulas. That means you can work in either metric or US customary units without manually converting first. For consistency in medical documentation, the final result is displayed in m².
Interpreting the result
A BSA result is usually interpreted as a body size estimate, not as a diagnosis or treatment order by itself. For adults, many values often fall roughly in the range of about 1.5 to 2.3 m², but this is only a broad orientation range and should not be used as a strict threshold. A small difference between formulas, such as 0.01 to 0.03 m², may be mathematically real but clinically unimportant depending on context. In other scenarios, especially when high-risk drugs are involved, even modest calculation differences may justify confirmation using institutional protocols.
It is also important to remember that BSA-based dosing has known limitations. Body composition, organ function, age, edema, sarcopenia, obesity, and disease state can all affect how a patient handles medications. This is one reason why modern precision medicine often combines BSA with laboratory values, toxicity monitoring, pharmacokinetic data, and specialist oversight.
Clinical context: BSA, BMI, and ideal body weight are not the same
People sometimes confuse BSA with BMI or ideal body weight, but these metrics answer different questions:
| Measurement | Main inputs | Typical unit | Primary purpose |
|---|---|---|---|
| BSA | Height and weight | m² | Scaling body size for selected medical calculations and dosing conventions. |
| BMI | Height and weight | kg/m² | Screening measure related to body size category and adiposity trends. |
| Ideal body weight | Usually height and sex-based formulas | kg | Reference estimate sometimes used in ventilation, dosing, and nutritional assessment. |
Although these metrics may all use height and weight in some form, they are not interchangeable. BSA is specifically trying to estimate body surface area, while BMI is a ratio and ideal body weight is a reference target estimate. Using the wrong metric in a medical calculation can lead to incorrect assumptions, so always verify which method is required.
Known limitations of BSA formulas
No BSA formula is perfect. All of them are statistical approximations created from population data, and all can become less reliable at body size extremes. This includes very low birth weight infants, severely obese adults, patients with amputations, and individuals with unusual body proportions. In these situations, formula choice may matter more, and direct clinical oversight becomes especially important.
- Formulas may differ slightly because they were derived from different study samples.
- Older formulas may not reflect the diversity of modern populations.
- BSA does not directly measure lean mass, fat mass, or organ function.
- Drug dosing based only on BSA may not capture toxicity risk or therapeutic response.
Reference data and authoritative sources
For additional evidence-based guidance, review information from recognized public and academic institutions. The following resources are useful starting points:
- National Cancer Institute for oncology treatment background and cancer care references.
- National Center for Biotechnology Information for published clinical studies and reviews on body surface area and dosing.
- MedlinePlus for patient-friendly educational material from the U.S. National Library of Medicine.
What the research generally shows about formula differences
Across average adult body sizes, the most common BSA equations usually cluster closely together. In everyday use, the difference between Mosteller and Du Bois is often small enough that it does not change routine interpretation. That said, outliers matter. As height and weight become more extreme, formulas can diverge more noticeably. This is one reason institutional preference matters. A clinic may standardize one formula not because every other formula is wrong, but because standardization improves consistency across teams, medication verification, and documentation workflows.
Historically, the Du Bois equation was highly influential, yet modern practice often favors Mosteller because it is easier to calculate and has acceptable agreement in many settings. Haycock is often respected for pediatric applications, while Boyd and Gehan and George are useful for comparative and research-oriented review. The best formula is often the one required by the clinical protocol you are following.
Frequently asked questions about BSA calculation
Is Mosteller more accurate than Du Bois?
Not universally. Mosteller is often preferred because it is simple and practical, and for many adults it gives a result very close to Du Bois and other formulas. Accuracy depends on the patient population and the reference standard being used.
Can I use pounds and inches?
Yes. This calculator accepts inches and pounds, then converts them internally to centimeters and kilograms before calculating BSA.
Why are there several BSA formulas?
Different investigators developed equations from different measurement datasets and mathematical approaches. Each equation reflects the assumptions and source population used in its derivation.
Is BSA the same as total body surface area in burns?
Not exactly. Burn assessment commonly uses the percentage of total body surface area affected. That concept is related to body surface area, but the bedside burn estimate itself uses additional clinical tools such as the Rule of Nines or Lund and Browder charts.
Should medication dosing always be based on BSA?
No. Many medications are dosed by weight, fixed dose, renal function, age, or therapeutic monitoring. BSA-based dosing is common in selected specialties, especially oncology, but it is not universal.
Bottom line
A high-quality BSA formula calculator should do three things well: convert units correctly, apply the selected equation accurately, and help you compare formulas in a transparent way. This page is designed for exactly that purpose. You can calculate BSA using Mosteller, Du Bois, Haycock, Gehan and George, or Boyd, then review how closely the formulas align for a specific patient. In practical medicine, the numeric result matters, but context matters more. Always match the formula to the protocol, verify unusual values, and use BSA as one component of a broader clinical decision.