Health & Medicine · Pharmacokinetics & Dosing
Body Surface Area Calculator
Calculates body surface area (BSA) in square metres using the Mosteller, DuBois & DuBois, or Haycock formula from height and weight.
Calculator
Formula
BSA = body surface area in square metres (m²). H = height in centimetres (cm). W = weight in kilograms (kg). The Mosteller formula uses a simple square-root approach widely adopted in oncology. The DuBois & DuBois formula (1916) is the historical clinical standard. The Haycock formula is preferred for neonates and children due to its validation in paediatric populations.
Source: Mosteller RD. N Engl J Med 1987;317:1098. DuBois D & DuBois EF. Arch Intern Med 1916;17:863–871. Haycock GB et al. J Pediatr 1978;93:62–66.
How it works
Unlike body weight alone, body surface area accounts for both height and weight simultaneously, producing a size metric that correlates more reliably with physiological parameters such as metabolic rate, glomerular filtration, and cardiac index. Many cytotoxic drugs — including carboplatin, cisplatin, doxorubicin, and paclitaxel — are dosed in mg/m² rather than mg/kg to reduce inter-patient variability in toxicity and efficacy. BSA is also used to calculate the cardiac index (cardiac output divided by BSA) and to index glomerular filtration rate to the standard 1.73 m² reference surface area.
Three validated formulas are offered. The Mosteller formula (1987) is BSA = √(H × W / 3600), where H is in cm and W is in kg. Its simplicity and accuracy in adults have made it the default in most oncology protocols and pharmacy software. The DuBois & DuBois formula (1916) is BSA = 0.007184 × H^0.725 × W^0.425 and was derived from direct surface measurements in nine individuals; it remains embedded in many legacy clinical references despite its small derivation sample. The Haycock formula (1978) is BSA = 0.024265 × H^0.3964 × W^0.5378, derived from a broader cohort including neonates and children, making it the preferred choice in paediatric and neonatal medicine.
In practice, the three formulas agree closely for adults of average build, typically differing by less than 2–3%. Discrepancies widen at extremes of size — obese adults, preterm neonates, or cachectic patients — so formula selection matters most in these populations. The Mosteller formula is recommended for general adult use due to its simplicity and widespread validation.
Worked example
Consider a patient who is 170 cm tall and weighs 65 kg. Using the Mosteller formula:
BSA = √(170 × 65 / 3600) = √(11050 / 3600) = √3.0694 = 1.75 m²
Using the DuBois formula: BSA = 0.007184 × 170^0.725 × 65^0.425 = 0.007184 × 47.23 × 5.17 ≈ 1.75 m²
Using the Haycock formula: BSA = 0.024265 × 170^0.3964 × 65^0.5378 = 0.024265 × 8.41 × 8.54 ≈ 1.74 m²
All three formulas produce nearly identical results for this average-sized adult. If this patient were prescribed a chemotherapy drug at 75 mg/m², the calculated dose would be 75 × 1.75 = 131.25 mg, typically rounded to the nearest standard vial size per institutional protocol.
Limitations & notes
BSA calculations carry inherent limitations that clinicians must recognise. First, all formulas were derived from relatively small and often non-representative samples; the DuBois formula, for example, was based on only nine subjects. Second, BSA does not capture body composition — two patients with identical BSA values may differ dramatically in lean mass and adipose tissue, affecting drug distribution and clearance. Third, dosing by BSA reduces but does not eliminate pharmacokinetic variability; area-under-the-curve (AUC) based dosing (as used for carboplatin via the Calvert formula) may provide more precise dose individualisation for some agents. Fourth, at extremes of weight — morbid obesity or severe malnutrition — BSA-based dosing may lead to overdosing or underdosing; some oncology protocols cap BSA at 2.0 m² or use adjusted body weight in obese patients. This calculator is intended as a clinical decision-support aid and does not replace the judgement of a qualified healthcare professional.
Frequently asked questions
Which BSA formula is most accurate for adults?
The Mosteller formula is the most widely recommended for general adult use. Studies comparing multiple formulas have found that Mosteller, DuBois, and Haycock produce results within 2–3% of each other for adults of average build. Mosteller is favoured for its computational simplicity and broad validation across diverse adult populations.
Which BSA formula should I use for children and neonates?
The Haycock formula (1978) is the standard choice for paediatric and neonatal patients. It was derived from a dataset that explicitly included infants and children, giving it better accuracy at the lower end of the size spectrum compared to the DuBois formula, which was validated only in adults.
What is a normal body surface area for an adult?
The reference BSA used in clinical medicine is 1.73 m², which is the historical average for adults of moderate build. In practice, BSA values for healthy adults typically range from approximately 1.5 m² in smaller women to 2.2 m² in larger men. The 1.73 m² standard is used to normalise GFR measurements.
Why is BSA used for chemotherapy dosing instead of body weight?
Early pharmacological studies in the 1950s–1960s showed that the maximum tolerated dose of many cytotoxic drugs correlated better with BSA than with body weight across species. BSA integrates both height and weight, providing a proxy for metabolic surface area and renal clearance. However, evidence for its superiority over weight-based dosing in humans is less definitive than originally believed, and some protocols now use fixed dosing or AUC-based approaches.
How is BSA used to calculate cardiac index?
Cardiac index (CI) is calculated by dividing cardiac output (CO, in L/min) by BSA (in m²): CI = CO / BSA. It normalises cardiac output for body size, allowing comparison between patients of different builds. A normal cardiac index is 2.5–4.0 L/min/m². Haemodynamic monitoring in ICU and cardiac catheterisation labs routinely reports cardiac index alongside cardiac output.
Last updated: 2025-01-15 · Formula verified against primary sources.