Which BSA formula should I use?

For adult oncology drug dosing, Mosteller (1987) is the most widely used because it is accurate, simple and has been validated in large populations. DuBois and DuBois (1916) remains the historical gold standard used in many laboratory reference ranges. For children and neonates, Haycock (1978) is generally preferred. If you are working with Asian populations, Fujimoto (1968) was specifically validated in that group.

What is the Mosteller formula for BSA?

The Mosteller formula is: BSA (m²) = sqrt(height_cm × weight_kg / 3600). It can also be written as sqrt((height_cm / 100) × weight_kg) after factoring out the metre conversion. It was published in the New England Journal of Medicine in 1987 and is now the default formula in most oncology dose-calculation software.

Why do the six formulae give slightly different results?

Each formula was derived by fitting a power-law regression to a different patient cohort measured in a different era. The differences are usually less than 5% for average-sized adults, but can diverge more at the extremes of height or weight, and particularly in children. No single formula is definitively correct — they are all approximations of a complex biological measurement.

How is BSA used in drug dosing?

Many cytotoxic chemotherapy agents, some antibiotics, and paediatric drug doses are expressed in mg/m² to account for the fact that drug metabolism and organ function scale more closely with body surface area than with body weight alone. A clinician multiplies the target dose per m² by the patient's BSA to obtain the total dose. This calculator gives the BSA component only — dose calculations must be performed and verified by a qualified prescriber or pharmacist.

What is the average BSA for an adult?

The commonly cited reference value is 1.73 m² for a 70 kg adult of average height (roughly 170 cm). However, this is only a rough guide. Women typically fall in the range 1.6–1.7 m² and men 1.7–1.9 m², depending on height and weight. Many drug-dosing tables use 1.73 m² as the normalisation denominator when expressing doses per m².

Is this calculator suitable for children and infants?

The calculator supports the Haycock formula, which was specifically validated in a paediatric cohort including neonates. For very small infants (below about 3 kg), all formulae become less reliable and clinical pharmacokinetic modelling is usually preferred. Always consult a paediatrician or clinical pharmacist for paediatric dosing.

Body Surface Area (BSA) Calculator

Body surface area (BSA) is one of the most important measurements in clinical medicine. Unlike body weight, it correlates more directly with cardiac output, renal clearance, basal metabolic rate, and the distribution of many drugs — which is why chemotherapy, immunosuppressant, and paediatric doses are routinely expressed in milligrams per square metre (mg/m²) rather than per kilogram.

This calculator implements all six major validated formulae and shows results side by side, so you can instantly see how they agree — or diverge — for a specific patient.

Educational, not medical advice. All BSA values produced here are estimates intended for educational and informational purposes. Actual drug prescribing decisions must be made by a qualified healthcare professional using verified clinical data and local dosing guidelines.

How it works

Every formula takes height (in centimetres) and weight (in kilograms) and returns a BSA in square metres. The calculator accepts either metric or imperial input and converts internally.

Mosteller (1987) — the oncology standard:

BSA = sqrt(height_cm * weight_kg / 3600)

The division by 3600 is equivalent to dividing height by 100 (converting to metres) and then taking the geometric mean of height in metres and weight in kilograms. It is fast to compute mentally and has been shown to give results within 2–3% of direct surface-area measurements.

DuBois and DuBois (1916) — the original reference:

BSA = 0.007184 * height_cm^0.725 * weight_kg^0.425

This power-law regression was fitted to direct body surface measurements on nine cadavers in 1916. Despite its small derivation sample, it has become the benchmark against which other formulae are compared.

Haycock (1978) — paediatric populations:

BSA = 0.024265 * height_cm^0.3964 * weight_kg^0.5378

Derived in a cohort that included neonates and infants, giving better accuracy at low weight and height than the adult-derived formulae.

Gehan and George (1970), Boyd (1935), and Fujimoto (1968) are three further validated models included for comparison. Fujimoto was specifically validated in Japanese subjects and may be more appropriate for Asian populations.

Worked example

A patient is 5 ft 8 in tall (172.7 cm) and weighs 75 kg:

Mosteller: sqrt(172.7 * 75 / 3600) = sqrt(3.597) = 1.897 m²
DuBois: 0.007184 * 172.7^0.725 * 75^0.425 = 1.898 m²
Haycock: 0.024265 * 172.7^0.3964 * 75^0.5378 = 1.916 m²

All three agree within about 1% here. At extremes — very short or very tall, underweight or obese — the spread can reach 10–15%, which is clinically significant for high-toxicity drugs.

Height	Weight	Mosteller	DuBois	Haycock
160 cm	55 kg	1.564 m²	1.567 m²	1.580 m²
170 cm	70 kg	1.826 m²	1.823 m²	1.843 m²
180 cm	85 kg	2.062 m²	2.059 m²	2.081 m²
190 cm	100 kg	2.299 m²	2.298 m²	2.320 m²

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