🧍 Body Surface Area Calculator

Calculate your Body Surface Area (BSA) in m² using three clinically validated formulas — Du Bois, Mosteller, and Haycock. BSA is widely used in medicine for drug dosing, burn assessment, and cardiac output calculations.

Height (cm)

Weight (kg)

What is Body Surface Area (BSA)?

Body Surface Area (BSA) is the total surface area of the human body, measured in square metres (m²). The average adult BSA is approximately 1.7 m². Unlike BMI, which only uses height and weight, BSA is used in medical and pharmacological contexts where the surface area of the body — rather than its mass — determines physiological parameters. BSA correlates better than body weight with cardiac output, blood volume, kidney function, and metabolic rate in many clinical contexts.

The most important clinical application of BSA is chemotherapy dosing. Many cytotoxic drugs are dosed in mg/m² of BSA because this normalises for differences in drug distribution across people of different sizes, reducing the risk of under-dosing (ineffective) or over-dosing (toxic). BSA-based dosing is also used for immunosuppressants, some cardiac drugs, and in paediatric medicine where weight-based dosing alone may be insufficient to account for developmental differences.

Several mathematical formulas estimate BSA from height and weight, as direct measurement is impractical. The most widely used is the Du Bois & Du Bois formula (1916), followed by the Mosteller formula (1987), which is favoured for its simplicity (BSA = √(height × weight / 3600) using cm and kg). Different formulas can yield BSA values that differ by 5–10%, so always use the formula specified by the clinical protocol in medical settings.

BSA Formulas

Du Bois & Du Bois (1916) — Most widely used

BSA = 0.007184 × H^0.725 × W^0.425

Mosteller (1987) — Simplest formula

BSA = √(H × W / 3600)

Haycock (1978) — Preferred for pediatrics

BSA = 0.024265 × H^0.3964 × W^0.5378

Where H = height in cm, W = weight in kg. All formulas return BSA in m².

How to Use the BSA Calculator

1

Choose Your Unit System

Select Metric (cm / kg) or Imperial (ft + in / lbs). The calculator handles unit conversion automatically.
2

Enter Height

In metric, enter your height in centimetres. In imperial, enter feet and inches in the two separate fields.
3

Enter Weight

Enter your body weight in kilograms or pounds depending on the selected unit system.
4

View Your BSA

See BSA results from all three formulas and their average, plus a clinical interpretation of your result.

Example Calculation

A person who is 170 cm tall and weighs 70 kg:

Du Bois = 0.007184 × 170^0.725 × 70^0.425 = 1.78 m²

Mosteller = √(170 × 70 / 3600) = 1.77 m²

Haycock = 0.024265 × 170^0.3964 × 70^0.5378 = 1.78 m²

Average BSA = 1.78 m²

Medical Uses of BSA

BSA is preferred over weight alone for many clinical applications because it better accounts for differences in body size and composition:

•Chemotherapy dosing: Most cytotoxic drugs are dosed in mg/m² to standardise exposure across patients of different sizes, reducing toxicity risk.
•Burns assessment: The Rule of Nines uses BSA to estimate the percentage of body surface affected by burns, guiding fluid resuscitation.
•Cardiac output: Cardiac index (CI = cardiac output / BSA) normalises heart function measurements for patient size.
•Renal function: GFR is often expressed per 1.73 m² (average adult BSA) to allow comparison between individuals.

Note: This calculator is for informational purposes only. Always consult a healthcare professional for clinical dosing decisions.

How the Body Surface Area Calculator Works

Formula, assumptions, and calculation steps for this health tool.

Methodology

Health calculators use published screening formulas and common planning rules to estimate body, nutrition, pregnancy, or fitness metrics from user inputs.

Calculation Steps

Enter the personal measurements requested by the tool.
Convert height, weight, age, dates, or activity inputs to standard units.
Apply the health or fitness formula for the selected metric.
Show the estimate with practical ranges or interpretation where available.

Assumptions and Limits

Results are educational estimates, not diagnosis or medical advice.
Individual factors such as medication, pregnancy, and medical history can change interpretation.
Consult a clinician for personal health decisions.

Reference basis: Common public-health and sports-science screening formulas.

Frequently Asked Questions

What is Body Surface Area (BSA)?

Body Surface Area (BSA) is the measured or calculated surface area of a human body, expressed in square metres (m²). Unlike body weight, BSA provides a better representation of body size because it accounts for both height and weight. The average adult BSA is approximately 1.7–1.9 m².

Why is BSA used instead of weight for drug dosing?

BSA-based dosing provides more consistent drug exposure across patients of varying sizes. Body weight alone does not scale proportionally with drug distribution and metabolism, especially for chemotherapy agents. Dosing by BSA (mg/m²) reduces the risk of under-dosing (reducing efficacy) or over-dosing (increasing toxicity) in patients who are significantly larger or smaller than average.

What is the normal BSA for adults?

The reference BSA used in medicine is 1.73 m², based on average values from historical studies. In practice, the typical range is 1.6–2.0 m². Average adult males tend to have a BSA of approximately 1.9 m², while adult females average around 1.7 m². Children have lower BSA values that increase progressively with age and growth.

Which BSA formula is most accurate?

No single formula is definitively most accurate for all populations. The Du Bois formula (1916) is historically the most widely used in clinical practice and pharmacology. The Mosteller formula is the simplest to calculate mentally and is popular in oncology. The Haycock formula performs particularly well in paediatric populations. For most adults, all three formulas give very similar results, usually within 2–3% of each other.

Real-World Applications

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Chemotherapy Dosing

Oncologists dose many cytotoxic agents (carboplatin, cisplatin, doxorubicin) in mg/m² of BSA to normalise drug distribution across patients of different sizes, balancing efficacy and toxicity.

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Burns Treatment

The "Rule of Nines" and Lund-Browder chart divide the body's surface area into percentages to assess burn coverage. BSA is critical for calculating fluid resuscitation volumes (Parkland formula).

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Paediatric Drug Dosing

In children, BSA-based dosing is more accurate than weight-based dosing for many drugs because it better accounts for the metabolic and physiological differences between children and adults.

❤️

Cardiac Physiology

Cardiac index (CI = cardiac output / BSA) normalises heart function measurements for body size, allowing comparison between patients of different stature in intensive care settings.

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Parenteral Nutrition

BSA is used alongside metabolic rate estimates to calculate total parenteral nutrition (TPN) requirements for patients with severe gastrointestinal conditions who cannot absorb nutrients orally.

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Pharmacokinetic Research

Clinical pharmacologists use BSA in population pharmacokinetic models to study how drug clearance, volume of distribution, and half-life scale across individuals of different body size.

Common Mistakes

Mixing Unit Systems

Different BSA formulas use different unit conventions. The Du Bois formula uses centimetres and kilograms. The Mosteller formula uses centimetres and kilograms under a square root. Always verify the required units before plugging in values.

Choosing the Wrong Formula

Each formula can give BSA values that differ by 5–10%. In clinical settings, always use the formula specified in the treatment protocol or drug product information — do not substitute without guidance.

Forgetting to Update BSA During Treatment

Patients undergoing chemotherapy often lose significant weight. BSA should be recalculated before each treatment cycle, as a change of more than 10% may warrant dose adjustment.

Using BSA for All Drug Dosing

Not all drugs are best dosed by BSA. Many medications (antibiotics, anticoagulants) are better dosed by weight, renal function, or flat dose. BSA dosing is specific to the drug class — verify before applying.

Ignoring Extreme Body Habitus

BSA formulas were developed from populations of average build. For severely obese patients, BSA-based dosing of some drugs may lead to overdose. Some protocols cap BSA at a maximum value (e.g. 2.0 m²) for this reason.

BSA Formula Comparison

Formula	Year	Equation (cm, kg)	Notes
Du Bois & Du Bois	1916	0.007184 × H⁰·⁷²⁵ × W⁰·⁴²⁵	Historic gold standard
Mosteller	1987	√(H × W / 3600)	Simplest; widely used clinically
Haycock	1978	0.024265 × H⁰·³³⁶⁴ × W⁰·⁵³⁷⁸	Validated for paediatric use
Gehan & George	1970	0.0235 × H⁰·⁴²²⁴⁶ × W⁰·⁵⁵⁵¹⁶	Common in oncology protocols
Boyd	1935	Complex formula	Children and infants

References

Du Bois, D. & Du Bois, E. F. A Formula to Estimate the Approximate Surface Area if Height and Weight be Known. Archives of Internal Medicine, 1916.
Mosteller, R. D. Simplified Calculation of Body Surface Area. New England Journal of Medicine, 1987.
Haycock, G. B. et al. Geometric Method for Measuring Body Surface Area. Journal of Pediatrics, 1978.
Baker, S. D. et al. Role of Body Surface Area in Dosing of Investigational Anticancer Agents. Journal of the National Cancer Institute, 2002.
Gurney, H. Dose Calculation of Anticancer Drugs: A Review of the Current Practice and Introduction of an Alternative. Journal of Clinical Oncology, 1996.