What BSA means

Body Surface Area (BSA) is the calculated total external area of the human body, expressed in square metres (m²). The average adult has a BSA of roughly 1.6–2.0 m², with 1.73 m² historically used as the standard adult reference (this is also what eGFR / kidney function values are normalised to).

BSA matters because many physiological quantities scale better with surface area than with weight alone:

• Chemotherapy dosing — most cytotoxic regimens are dosed in mg/m² to balance efficacy and toxicity across patients of different sizes.
• Cardiac output indexing — cardiac index = cardiac output ÷ BSA, allowing comparison across body sizes.
• Pediatric drug dosing — pediatric maintenance fluids, dosages, and burn-fluid resuscitation rules (e.g. Parkland) all use BSA.
• Burn assessment — "% total body surface area" burned drives the resuscitation calculation.
• Glucocorticoid stress dosing, transplant immunosuppressant titration, and many radiation therapy plans.

The three formulas, in plain English

No formula directly measures BSA — they are all empirical regressions fit to cadaver and live-subject measurements over the past century. Different formulas were validated on different populations, which is why three remain in common use.

Mosteller (1987)

BSA (m²) = √( height_cm × weight_kg / 3600 )

The most-cited modern formula. Published as a one-page letter to the New England Journal of Medicine in 1987 by R.D. Mosteller. Its appeal is that it's accurate and memorable — most chemo nomograms today use Mosteller because clinicians can do it on a napkin if they have to. Accurate across a wide range of body types, including obese patients where DuBois under-predicts.

DuBois & DuBois (1916)

BSA (m²) = 0.007184 × height_cm^0.725 × weight_kg^0.425

The historical gold standard. Derived in 1916 from just nine cadaver measurements — and yet remarkably durable for normal-weight adults. Tends to underestimate BSA in obese patients (because none were in the original sample). Still used in older oncology protocols and in cardiology software because of inertia. Cross-checking with Mosteller is wise above BMI ~30.

Haycock (1978)

BSA (m²) = 0.024265 × height_cm^0.3964 × weight_kg^0.5378

The pediatric workhorse. Published by G.B. Haycock et al. specifically for neonates, infants and children, validated on 81 subjects from premature babies to teenagers. The DuBois formula's underestimate is worst at the smallest body sizes; Haycock corrects it. Many pediatric chemotherapy and dialysis calculations specify Haycock by name.

When the formulas disagree

For a typical adult (170 cm, 70 kg), the three formulas usually agree within ±2%. The disagreements grow at the extremes:

• Obese patients (BMI 35+): Mosteller > DuBois. Use Mosteller, or check institutional policy — some centres cap BSA at 2.0 m² for chemo regardless of formula.
• Underweight / cachectic patients: DuBois may overestimate slightly; Mosteller is still reasonable.
• Children, especially infants: Haycock is the standard. DuBois & Mosteller both diverge here.

When in doubt, calculate with all three (this tool shows all at once) and use the one your hospital's protocol specifies. If the protocol is silent, Mosteller is the safest modern default for adults and Haycock for children.

Educational reference only

This calculator exists to help you double-check a number, learn the formulas, or teach them — not to be the source of truth for a patient care decision. Always confirm with a licensed clinician, follow your institution's protocol, and refer to the primary literature for any high-stakes calculation.