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About this tool
Estimate body surface area (BSA) using the Mosteller and Du Bois formulas.
The Body Surface Area Calculator converts a height in centimetres and a weight in kilograms into BSA in square metres, using the Mosteller formula — the square root of height times weight divided by 3600 — and showing the Du Bois result, 0.007184 x height^0.725 x weight^0.425, alongside it. BSA is the figure many drug doses, cardiac indices and burn assessments are scaled to, so students, nurses and anyone checking a calculation need it in a hurry. It reports both formulas because they do not always agree, and it is an arithmetic aid, not a dosing authority.
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Type the weight in kilograms into the 'Weight (kg)' field, which starts pre-filled with 70.
Type the height in centimetres into the 'Height (cm)' field, which starts at 175 — there is no Calculate button, the figures recompute on every keystroke.
Read the Mosteller estimate as the headline result ('1.84 m²' at those defaults, captioned 'Mosteller formula') with the 'Du Bois formula' value ('1.85 m²') in the box beneath it; enter 0 or less in either field and the panel falls back to '—' with 'Enter weight and height'.
Shows the Mosteller and Du Bois results side by side so you can see whether the choice of formula changes anything material for this patient.
Leads with Mosteller, the square-root form adopted in most clinical settings precisely because it is simple enough to check by hand.
Height in centimetres and weight in kilograms are all it needs — no age, sex or body-composition assumptions enter the calculation.
BSA in square metres equals the square root of (height in cm x weight in kg) / 3600. For a person 175 cm and 70 kg that is the square root of 3.403, or about 1.84 m². Its appeal is that it can be worked out on a basic calculator, which is why it became the clinical default.
Du Bois uses a power relationship — 0.007184 x height^0.725 x weight^0.425 — derived from a 1916 study of only nine subjects, while Mosteller is a later square-root simplification. For average adults the two land within a few percent of each other, but they diverge more at very high or very low body weights, which is why both are shown here.
Because BSA correlates better than body weight alone with metabolic rate, blood volume and renal clearance, so several drug classes — cytotoxic chemotherapy in particular — are prescribed in mg per square metre. Which formula and which dose apply to a given patient is a prescriber's decision; this tool only performs the arithmetic.
No — the inputs are centimetres and kilograms, so convert first: multiply inches by 2.54 for centimetres and pounds by 0.4536 for kilograms. Entering imperial figures directly will produce a BSA that is badly wrong rather than an error message, so check the units before reading the result.
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