Body Surface Area Calculator
Calculates your body surface area (BSA) in m² using the DuBois formula from weight and height. Clinicians use BSA to determine chemotherapy doses, cardiac index, and burn coverage.
About this calculator
Body Surface Area (BSA) is the total skin area of the human body, expressed in square metres. It is widely used in medicine because many physiological variables — such as cardiac output, renal clearance, and drug dosing — scale more reliably with BSA than with body weight alone. This calculator applies the DuBois & DuBois formula (1916), one of the most commonly used in clinical practice: BSA (m²) = 0.007184 × weight_kg^0.425 × height_cm^0.725. The exponents reflect the non-linear relationship between linear body dimensions and skin area. Average BSA for an adult is approximately 1.7–1.9 m². Other formulas exist (Mosteller, Haycock), but DuBois remains a standard reference in oncology and cardiology.
How to use
Consider a patient weighing 70 kg with a height of 170 cm. Apply the DuBois formula: BSA = 0.007184 × 70^0.425 × 170^0.725. First, 70^0.425 ≈ 6.828; then 170^0.725 ≈ 37.16. Multiply: 0.007184 × 6.828 × 37.16 ≈ 0.007184 × 253.74 ≈ 1.823 m². This result (≈ 1.82 m²) is within the normal adult range and would be used, for example, to normalise a cardiac index or to calculate a weight-based chemotherapy dose per m².
Frequently asked questions
Why is body surface area used for chemotherapy dosing instead of body weight?
Body surface area correlates more closely with blood volume, organ size, and drug clearance rates than simple body weight does, which helps maintain consistent drug plasma concentrations across patients of different sizes. Using BSA reduces the risk of toxic overdose in smaller patients and underdosing in larger ones. This approach has been standard in oncology since the mid-20th century, though some newer targeted therapies use fixed flat dosing because their pharmacokinetics are less BSA-dependent. Clinicians typically use BSA together with renal and hepatic function when finalising chemotherapy regimens.
What is a normal body surface area for adults and children?
The average BSA for adult men is approximately 1.9 m² and for adult women approximately 1.6–1.7 m². Newborns have a BSA of roughly 0.25 m², and it increases steadily through childhood, reaching adult values in the mid-teens. Because children have a higher BSA-to-weight ratio than adults, weight-based dosing alone can underestimate drug requirements in paediatric patients. BSA-adjusted dosing is therefore particularly important in paediatric oncology and critical care.
How accurate is the DuBois formula compared to other BSA formulas?
The DuBois formula was derived from a small sample of nine subjects and can underestimate BSA in obese individuals by up to 5–8% compared to direct measurement methods. The Mosteller formula (BSA = √(height_cm × weight_kg / 3600)) is mathematically simpler and performs comparably for most adults, while the Haycock formula is preferred in paediatric settings. Direct measurement using 3D scanning is the most accurate method but is impractical clinically. For most adult patients, the DuBois, Mosteller, and Boyd formulas agree within about 2%, which is clinically acceptable.