Body Surface Area (BSA) Calculator

Formula

Mosteller: BSA (m²) = √((Height (cm) × Weight (kg)) ÷ 3600) Du Bois: BSA (m²) = 0.007184 × Weight (kg)^0.425 × Height (cm)^0.725

BSA represents body surface area in square meters (m²). Height must be provided in centimeters (cm) and weight in kilograms (kg). In the Mosteller formula, height and weight are multiplied, divided by the constant 3600, and the square root is extracted. In the Du Bois and Du Bois formula, empirical regression constants and fractional power exponents account for nonlinear variations between mass, stature, and actual skin surface area.

Worked example

Height

175

Weight

70

• BSA (Mosteller): 1.845 m²
• BSA (Du Bois): 1.848 m²

What Body Surface Area (BSA) Calculates

Body Surface Area (BSA) measures the total calculated exterior surface area of the human body, expressed in square meters (m²). While Body Mass Index (BMI) evaluates whether a person’s weight is proportional to their height, BSA provides a biological metric reflecting total skin surface and metabolic capacity.

Physiologists and healthcare clinicians utilize BSA across numerous specialties:

• Chemotherapy Dosing: Oncology protocols frequently dose antineoplastic agents per square meter (e.g., mg/m²) to avoid under-treating or causing systemic toxicity.
• Hemodynamic Indexing: Cardiac index and stroke volume index scale raw cardiac output against BSA to compare cardiovascular function fairly between large and small individuals.
• Renal Clearance Evaluation: Glomerular filtration rate (GFR) is typically standardized to a normalized human surface area of 1.73 m².
• Burn Assessment: Triage protocols quantify severe thermal injuries as a percentage of total body surface area to guide intravenous fluid resuscitation.

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Step-by-Step Worked Example

Consider an adult with the following measurements:

• Height: 175 cm
• Weight: 70 kg

1. Mosteller Formula

The Mosteller formula calculates BSA using the equation: $$\text{BSA} = \sqrt{\frac{\text{Height (cm)} \times \text{Weight (kg)}}{3600}}$$

1. Multiply height by weight:
   $$175 \times 70 = 12{,}250$$
2. Divide by the constant 3600:
   $$\frac{12{,}250}{3600} \approx 3.402778$$
3. Take the square root:
   $$\sqrt{3.402778} \approx 1.845\text{ m²}$$

2. Du Bois and Du Bois Formula

The classic Du Bois formula uses exponential weights derived from clinical measurements: $$\text{BSA} = 0.007184 \times \text{Weight (kg)}^{0.425} \times \text{Height (cm)}^{0.725}$$

1. Calculate the weight component:
   $$70^{0.425} \approx 6.0725$$
2. Calculate the height component:
   $$175^{0.725} \approx 42.3458$$
3. Multiply together with the empirical constant:
   $$0.007184 \times 6.0725 \times 42.3458 \approx 1.848\text{ m²}$$

Both formulas align closely, differing by only 0.003 m² in this standard adult profile.

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How to Interpret BSA Results

Unlike body fat percentage or BMI, BSA does not have a single "ideal" or "healthy" target number because human stature varies naturally across populations. Instead, calculated values are interpreted relative to physiological benchmarks and clinical standards:

• Average Adult Woman: Typically ranges between 1.6 m² and 1.8 m² (standard benchmark ~1.7 m²).
• Average Adult Man: Typically ranges between 1.8 m² and 2.0 m² (standard benchmark ~1.9 m²).
• Clinical Reference Standard: Medical physiology frequently uses 1.73 m² as the universal baseline reference for normalizing laboratory clearances such as eGFR.
• Pediatric Values: An infant may have a BSA of approximately 0.25 m², while a 10-year-old child often averages around 1.0 m² to 1.1 m².

Evaluating Height Sensitivity

Body composition and stature influence how mass is distributed across surface area. Holding weight constant at 70 kg illustrates the impact of vertical frame:

• Lower Height (140 cm): BSA (Mosteller) = 1.65 m²
• Base Example (175 cm): BSA (Mosteller) = 1.845 m²
• Higher Height (210 cm): BSA (Mosteller) = 2.021 m²

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Practical Measurement Tips

1. Ensure Standardized Measurement Conditions: Record standing height flat-footed against a flat wall or stadiometer. Obtain weight in light clothing before fluid intake or meals.
2. Double-Check Input Units: Confirm your units are metric. To convert pounds to kilograms, divide by 2.20462. To convert inches to centimeters, multiply by 2.54.
3. Maintain Consistency Across Treatment Protocols: While Mosteller and Du Bois produce near-identical values for typical body shapes, clinicians should stick to one formula throughout a patient's therapeutic course to prevent small calculation variances.

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When Not to Rely on Standard BSA Formulas

While BSA estimates are robust for the general population, mathematical formulas possess inherent limitations in specific clinical conditions:

• Severe Edema or Ascites: Large amounts of fluid accumulation increase measured weight dramatically without reflecting true functional tissue surface area.
• Major Limb Amputations: Standard formulas assume an intact anatomical frame; patients with amputations require proportional deduction tables based on missing body segments.
• Extreme Morbid Obesity: Highly elevated adipose stores can cause certain BSA equations to overestimate metabolic capacity, prompting clinicians to consider adjusted dosing weights.
• Neonatal Medicine: Premature infants have unique surface-to-volume ratios that often require specialized pediatric nomograms or pharmacokinetic modeling rather than generalized adult equations.

Comparison

Scenario	Input	Result
Lower input	Height: 140	BSA (Mosteller): 1.65 m²
Base example	Height: 175	BSA (Mosteller): 1.845 m²
Higher input	Height: 210	BSA (Mosteller): 2.021 m²

Common mistakes

• Entering height in inches or weight in pounds without converting to centimeters and kilograms first.
• Assuming body surface area (BSA) is identical to Body Mass Index (BMI), which measures weight-to-height ratio rather than surface area.
• Relying on standard adult formulas for neonates or severe amputees without specialized clinical adjustments.
• Using outdated weight values when calculating chemotherapy or narrow-therapeutic-index medication dosages.
• Confusing the Mosteller and Du Bois formulas, which may yield slight numerical differences in extreme body compositions.

Checklist

• Measure standing height accurately without shoes using centimeters.
• Weigh yourself on a calibrated scale in kilograms, preferably in the morning.
• Verify that units match the formula inputs (metric: cm and kg).
• Identify which clinical protocol or formula your healthcare provider requests.
• Use current weight rather than ideal or historical weight for active dosing.
• Record values to at least two or three decimal places for clinical accuracy.

Calculators Percentage Editorial Team

Calculator guides from the Calculators Percentage team. These introductory examples are educational, not professional advice.

Last reviewed: November 12, 2026

This tool is for informational and educational purposes only and does not replace formal clinical evaluation. Never alter prescription drug dosages or medical treatments based on online estimates.