Body Surface Area (BSA) Calculator
Estimate your body surface area from height and weight, and see how the five classic formulas — Du Bois, Mosteller, Haycock, Gehan–George, and Boyd — compare side by side. BSA is the size measure medicine actually doses by: chemotherapy in mg/m², cardiac index, burn assessment, and the 1.73 m² standard behind kidney-function reporting.
Why medicine measures people in square meters
Skin area tracks the body’s metabolically active mass, blood volume, and heat exchange better than weight alone, so many clinical quantities scale by BSA. Because nobody can conveniently measure real skin area, height–weight formulas stand in for it. All five shown here take the form of a power law fit to direct measurements from different eras and samples. For typical adult sizes they land within a few percent of one another — the spread only becomes meaningful for infants, very small or very large bodies, which is exactly where clinicians choose their formula deliberately.
How it’s calculated
With W in kg and H in cm: Du Bois = 0.007184 × W0.425 × H0.725; Mosteller = √(W×H÷3600); Haycock = 0.024265 × W0.5378 × H0.3964; Gehan–George = 0.0235 × W0.51456 × H0.42246; Boyd = 0.03330 × W(0.6157 − 0.0188 log₁₀W) × H0.3. The headline number is the arithmetic mean of the five; 1 m² = 10.764 ft².
Educational estimates, not medical advice. Never compute or adjust a medication dose from an online BSA figure — dosing formulas, rounding rules, and caps are set by clinicians and pharmacists using your institution’s standard.
Typical BSA values
Standard reference averages; the 1.73 m² used to index eGFR is the adult average adopted from early 20th-century studies.
Worked example
An adult 5′10″ (177.8 cm) and 160 lb (72.6 kg): Du Bois 1.898 m², Mosteller 1.893, Haycock 1.895, Gehan–George 1.901, Boyd 1.897 — an average of 1.90 m² (about 20.4 ft²), with barely 0.4% separating the highest and lowest estimates.
Common mistakes
- Mixing units — every formula here expects kg and cm; the calculator converts US entries for you.
- Averaging formulas for a drug dose; clinics standardize on one equation, and dosing is their call.
- Using adult-fit formulas (like Du Bois) for infants, where Haycock or Mosteller behave better.
- Confusing BSA with BMI — BSA is area for scaling physiology; BMI is a weight-for-height screening index.
Where it is used
- Chemotherapy and some antibiotic/antiviral dosing in mg/m².
- Cardiac index: cardiac output divided by BSA.
- Indexing eGFR and other physiology to the 1.73 m² standard.
- Burn care (rule of nines applies percentages of BSA).
Frequently asked questions
Why are there so many BSA formulas?
Measuring skin area directly is hard, so each research group fit its own height–weight equation to a different sample: Du Bois (1916) to 9 subjects, Boyd (1935) to growth data, Gehan–George (1970) to 401 direct measurements, Haycock (1978) to infants through adults, and Mosteller (1987) simplified the math to √(height × weight ÷ 3600). Near average sizes they agree within a few percent.
Which formula do hospitals actually use?
Du Bois remains the classic reference and Mosteller is the workhorse in oncology and pediatrics because it is easy to compute and validate. Institutions standardize on one formula for consistency, so a chemotherapy dose is always checked against the clinic’s chosen equation — not an online average.
What is a normal body surface area?
Commonly used averages are about 1.6 m² for adult women and 1.9 m² for adult men, with the overall adult reference often quoted near 1.7 m². The 1.73 m² figure used to index kidney function (eGFR) is the average adult BSA adopted from early 20th-century studies. A newborn is around 0.25 m² and a ten-year-old around 1.14 m².
Why is BSA used for drug dosing instead of weight?
BSA tracks metabolically active mass and blood flow better than raw weight, so doses scale more consistently across body sizes — which is why chemotherapy is classically dosed in mg per m². It is imperfect at the extremes of size, and some narrow-therapeutic-index drugs use other methods, so dosing is always a clinician’s call.
Do these formulas work for children?
Haycock and Mosteller were validated down to infants and are the usual pediatric choices; Du Bois can underestimate small children. Pediatric dosing decisions belong with a clinician or pharmacist regardless of formula.