How this calculator works
BSA is an estimated external surface area. The equations were fitted in different samples and can disagree, especially at size extremes. Fujimoto has three original age bands; the other four outputs do not change with that selector. Oedema, amputations and measurement error can limit estimates. BSA alone does not select a medication or dose. The result is an estimate for information only and is not medical advice.
Formula
With W in kg and H in cm: Mosteller = sqrt(WH/3600); Du Bois = 0.007184 W^0.425 H^0.725; Haycock = 0.024265 W^0.5378 H^0.3964; Gehan-George = 0.0235 W^0.51456 H^0.42246. Fujimoto (m²): under 1, 0.009568 W^0.473 H^0.655; ages 1-5, 0.038189 W^0.423 H^0.362; ages 6+, 0.008883 W^0.444 H^0.663.
Worked example
At 180 cm and 80 kg, Mosteller gives sqrt(14400/3600) = 2.000 m². At 160 cm and 90 kg the same product also gives 2.000 m².
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Frequently asked questions
Why are the answers different?
Each equation is an empirical approximation with different coefficients and development data. They are not interchangeable in every protocol.
Can I use this for children?
Haycock included infants through adults. Select the correct Fujimoto age band; suitability still depends on the purpose and clinical context.
Is BSA the same as BMI?
No. BSA estimates area in square metres; BMI divides mass by height squared and has units of kg/m².