How this calculation works
Multiply the numerical centimetre height and kilogram weight, divide by the formula’s unit-specific constant 3,600, then take the square root. The output is an estimated surface area in square metres. Height or weight in a different unit must be converted first; the constant is not unchanged when the measurement system changes.
Mosteller BSA (m²) = √(height cm × weight kg / 3600)A worked example
At 180 cm and 80 kg, the intermediate value is 180×80/3600 = 4. Its square root is 2 m². This is a formula estimate, not a direct measurement of skin surface.
Good to know
Mosteller formula only. Body shape, unusual composition and clinical circumstances can limit an estimate. The tool does not calculate a medication dose, fluid prescription or absolute kidney clearance. Clinical protocols may require another method or additional checks.
Reference: Mosteller: simplified calculation of body surface area (opens in a new tab) ↗
The square root is part of the unit-specific equation
The Mosteller equation combines height in centimetres and weight in kilograms using the constant 3,600. The square root is essential: 180×80/3600 is four, but the estimated surface area is two square metres. The intermediate four should not be labeled as the final BSA.
The height converter can prepare centimetres from feet and inches before entry. Mixing a height in metres with the centimetre constant would produce the wrong result even if the number looked reasonable. The tool keeps the accepted units beside the fields and the output unit beside the result.
A surface-area estimate is not a dosing instruction
Body surface area is a modelled physical quantity. Some clinical protocols use it as one ingredient, but this calculator supplies no drug, dose, indication or adjustment rule. A mathematically correct surface area is not enough information to determine a safe clinical prescription.
The eGFR calculator reports a kidney estimate indexed to 1.73 m², which is another reason unit labels matter. An indexed rate and a person’s surface-area estimate are different quantities. Do not combine them casually to obtain a treatment instruction. Mosteller is also only one surface-area equation; individual body shape can differ from the populations behind such formulas.
A few questions, answered
Why is the result not height times weight divided by 3600?
That is the intermediate value; Mosteller takes its square root.
Can I enter metres for height?
Convert to centimetres first.
Will this tell me a medication dose?
No. It estimates surface area only.