Body Surface Area (BSA) Calculator

Body Surface Area formula based on height and weight

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What Is Body Surface Area?

Body Surface Area (BSA) estimates the total area of the external surface of the human body, measured in square meters (m²). Unlike body weight alone, BSA accounts for both height and weight, providing a more physiologically relevant measure for calculating drug dosages, estimating metabolic rate, indexing cardiac output, and assessing burn severity. The average adult BSA is approximately 1.7 m².

Worked Example

An oncologist needs to calculate BSA for a patient who is 170 cm tall and weighs 70 kg. Using the Mosteller formula, BSA = √(170 × 70 / 3600) = √(3.306) = 1.818 m². If the chemotherapy protocol calls for 75 mg/m², the dose would be 75 × 1.818 = 136.4 mg.

Formula Comparison

Mosteller (1987): The simplest and most widely used formula. It takes the square root of the product of height and weight divided by 3600. Preferred in most clinical settings due to its simplicity and adequate accuracy for adults and children.

DuBois & DuBois (1916): The original BSA formula, derived from measurements of only nine individuals. Despite its small derivation sample, it remains widely cited and validated across many populations. It tends to underestimate BSA in obese patients.

Haycock (1978): Developed specifically with pediatric patients in mind, this formula performs well across a wide range of body sizes from neonates to adults. It is often preferred for chemotherapy dosing in children.

Clinical Significance

BSA is critical in oncology for chemotherapy dose calculation, where many protocols express doses in mg/m². In cardiology, BSA is used to calculate Cardiac Index (CI = CO / BSA), which normalizes cardiac output to body size. Burn assessment uses BSA to estimate total body surface area affected, guiding fluid resuscitation via the Parkland formula. BSA-based dosing helps account for differences in drug metabolism across patients of varying sizes, potentially improving efficacy while reducing toxicity.

Frequently Asked Questions

Which BSA formula should I use?

For most adult clinical applications, the Mosteller formula is recommended due to its simplicity and accuracy. For pediatric patients, the Haycock formula may be more appropriate. The DuBois formula is historically significant but may underestimate BSA in obese individuals. Always follow your institution's protocol for the preferred formula.

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

BSA correlates more closely with metabolic rate and organ size than body weight alone. A tall, lean patient and a short, heavy patient with the same weight have different metabolic capacities. BSA-based dosing helps standardize drug exposure across diverse body compositions, particularly for drugs with narrow therapeutic windows like chemotherapy agents.

What is a normal BSA for an adult?

Average adult BSA ranges from approximately 1.6 to 1.9 m². For adult males, the average is about 1.9 m², while for adult females it is about 1.6 m². Neonates typically have a BSA of 0.2\u20130.25 m², and children's values fall between neonatal and adult ranges depending on age and size.

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