Body Surface Area Calculator - Estimate Your BSA Free BSA Calculator

What is Body Surface Area (BSA)?

Body surface area (BSA) is the measured or calculated total area of the outer surface of the human body, expressed in square metres (m²). BSA is a critically important parameter in clinical medicine used for drug dosing (especially chemotherapy and other weight-sensitive medications), calculating cardiac index, determining burn severity, estimating renal clearance, and adjusting fluid replacement therapy.

Unlike body weight alone, BSA accounts for both height and weight, providing a more accurate basis for scaling physiological processes. This free online BSA calculator uses five scientifically validated formulas — Du Bois, Mosteller, Haycock, Gehan-George, and Boyd — so you can compare results and choose the most appropriate one for your needs.

Key Features of This BSA Calculator

• Five Scientific Formulas: Calculates BSA using Du Bois, Mosteller, Haycock, Gehan-George, and Boyd methods simultaneously.
• Metric & Imperial Support: Enter height in centimetres or feet/inches, and weight in kilograms or pounds.
• Side-by-Side Comparison: View all five formula results in a comparison table to see how they differ.
• Primary Display: Highlights the Du Bois result as the most commonly referenced clinical value.
• Unit Conversion: Displays height and weight in both metric and imperial units for convenience.
• Instant Calculation: Get all five BSA results with a single click.

BSA Formulas — How Body Surface Area Is Calculated

How to Use This BSA Calculator — Step-by-Step

1. Choose Unit System: Toggle between Metric (cm/kg) and Imperial (ft-in/lbs).
2. Enter Your Height: Input height in centimetres, or in feet and inches if using imperial units.
3. Enter Your Weight: Input weight in kilograms or pounds.
4. Click "Calculate BSA": View your BSA from all five formulas, with Du Bois highlighted as the primary result.
5. Compare Results: Review the formula comparison table to see differences between methods.

Practical Examples of BSA Calculation

Example 1 — Adult male, 170 cm, 70 kg (Du Bois):

• BSA = 0.007184 × 170^0.725 × 70^0.425
• BSA = 0.007184 × 46.18 × 5.53 = 1.81 m²

Example 2 — Adult female, 160 cm, 55 kg (Mosteller):

• BSA = √(160 × 55 ÷ 3600) = √(2.444) = 1.56 m²

Example 3 — Child, 120 cm, 25 kg (Haycock):

• BSA = 0.024265 × 120^0.3964 × 25^0.5378
• BSA = 0.024265 × 9.37 × 5.55 = 0.93 m²

Clinical Uses of BSA — When to Use a BSA Calculator

• Chemotherapy Dosing: Many chemotherapy drugs are dosed per m² of BSA to account for body size variations and reduce toxicity risk.
• Cardiac Index Calculation: Cardiac output divided by BSA gives the cardiac index, a key metric for evaluating heart function relative to body size.
• Burn Assessment: The “Rule of Nines” uses BSA to estimate the percentage of body surface affected by burns for treatment planning.
• Renal Function: Glomerular filtration rate (GFR) is often normalised to 1.73 m² BSA for standardised comparison across patients of different sizes.
• Fluid Replacement: BSA is used to calculate maintenance fluid requirements, particularly in paediatric and burn patients.
• Metabolic Studies: Research on basal metabolic rate and energy expenditure often references BSA as a normalising factor.

Understanding Your BSA Results — Typical Values

• Newborn: ~0.25 m²
• Child (2 years): ~0.5 m²
• Child (10 years): ~1.14 m²
• Adolescent (15 years): ~1.5 – 1.7 m²
• Adult female (average): ~1.6 – 1.8 m²
• Adult male (average): ~1.8 – 2.0 m²
• Large adult: ~2.0 – 2.4 m²

The standard reference BSA of 1.73 m² is used as the normalisation factor for GFR and other clinical calculations.

Which BSA Formula Should I Use? — Tips & Best Practices

The choice of formula depends on the clinical context:

• Du Bois: The most widely used in clinical practice and the default in most medical references. Best choice for general adult use.
• Mosteller: Popular for its simplicity (easy mental calculation). Widely used in oncology for chemotherapy dosing.
• Haycock: Often preferred for paediatric patients as it was validated across a wide age range including infants and children.
• Gehan-George: Developed from a large dataset; provides results similar to Du Bois for most individuals.
• Boyd: One of the earliest formulas; less commonly used today but still referenced in some clinical guidelines.

In practice, the differences between formulas are usually small (<5%) for average adults. When precision matters (e.g., chemotherapy dosing), use the formula specified by the drug’s dosing guidelines.

Limitations & Medical Disclaimer

• Estimates Only: All BSA formulas are mathematical approximations. Actual body surface area can only be measured directly through 3D body scanning.
• Extreme Body Types: BSA formulas may be less accurate for individuals with extreme obesity, very low body weight, or amputations.
• Not a Diagnostic Tool: BSA values should be used as part of comprehensive clinical assessment, not in isolation.
• Paediatric Use: For children, the Haycock or Mosteller formula is generally preferred over Du Bois.

Disclaimer: This BSA calculator is provided for informational and educational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider before making any clinical decisions based on BSA calculations.

Frequently Asked Questions About BSA

Q: What is the average body surface area for an adult?

A: The average BSA is approximately 1.7 m² for women and 1.9 m² for men. The standard reference value of 1.73 m² is used for normalising GFR and other clinical measurements.

Q: Why is BSA used for drug dosing instead of just body weight?

A: BSA correlates more closely with many physiological parameters (cardiac output, renal clearance, metabolic rate) than body weight alone. This makes BSA-based dosing more accurate for medications with narrow therapeutic windows, like chemotherapy agents.

Q: Can I calculate BSA for my child?

A: Yes. This calculator works for all ages. For paediatric patients, the Haycock formula is generally considered the most appropriate. Simply enter the child’s height and weight to get results from all five formulas.

Q: Do the different BSA formulas give very different results?

A: For average-sized adults, the differences are typically less than 5%. However, at extremes of height or weight, differences may be more significant. Comparing all five formulas in the results table helps identify any notable variation.