Many medical doses are not set by weight alone. Chemotherapy drugs, burn treatments and some cardiac measurements are scaled to the total surface area of the body, because skin area tracks metabolic activity better than kilograms do. This calculator estimates your body surface area (BSA) from height and weight, giving the square-metre figure that clinicians use as a dosing and assessment reference.
Quick Answer
Using the widely used Mosteller formula: BSA (m²) = √( height in cm × weight in kg ÷ 3600 ). A typical adult result falls between about 1.6 and 1.9 m².
What Body Surface Area Is and Why It Is Calculated
Body surface area is exactly what the name suggests: the total area of the skin covering the body, expressed in square metres. Nobody measures it directly outside a research lab, so medicine relies on estimation formulas built from height and weight — the two measurements every clinic already takes. Two formulas dominate. The older Du Bois formula (1916) raises height and weight to fractional powers, which made it painful before computers. The Mosteller formula (1987) replaced it in most day-to-day practice because it needs only a square root, and studies show it agrees closely with Du Bois across ordinary adult body types.
The number matters because several high-stakes calculations are normalised to it. Chemotherapy agents are commonly dosed in milligrams per square metre, so the BSA figure directly sets how much drug a patient receives. Burn specialists estimate the percentage of body burned and fluid needs with BSA in the background. Cardiologists divide cardiac output by BSA to get the cardiac index, which lets them compare heart performance between a small adult and a large one fairly. In each case, BSA acts as a fairer "size" measure than weight alone, because two people of equal weight but different heights genuinely differ in body size.
BSA Beyond Drug Dosing
The surface-area figure quietly underpins several other clinical yardsticks. Kidney function results are standardised to a body surface area of 1.73 m² — roughly the average adult value found in early studies — which is why eGFR results carry that unit; a very large or very small person's true filtration can be re-scaled using their own BSA when precision matters. In burn care, clinicians first estimate what percentage of the surface is injured (the "rule of nines" divides the body into regions of roughly 9% each) and then use the total area to guide fluid resuscitation volumes.
Reference values help anchor a result. A newborn's BSA is only about 0.25 m²; a ten-year-old's is around 1.1 m²; typical adult figures cluster near 1.6 m² for women and 1.9 m² for men, with height influencing the total more than most people expect — two adults of identical weight, one 20 cm taller, differ measurably in surface area, which is one reason weight-only dosing can misjudge the tall, lean patient. Athletes and bodybuilders sit at the awkward edge of the formulas: their extra mass is muscle rather than the average tissue mix the equations were fitted on, so their calculated BSA tends to run slightly high relative to measured area.
How to Use This BSA Calculator
- Measure height without shoes, in centimetres (or convert from feet and inches first).
- Weigh yourself, or use a recent clinical weight, in kilograms.
- Enter the height and weight into the calculator.
- Read the estimated body surface area in square metres.
- For any dosing-related use, note which formula produced the figure, since results differ slightly between formulas.
- Recalculate after significant weight change — BSA moves with weight even when height does not.
Worked Example: An Average Adult
Take an adult who is 175 cm tall and weighs 70 kg. Multiply height by weight: 175 × 70 = 12,250. Divide by 3,600: 3.4028. Take the square root: 1.84 m². Running the same person through the older Du Bois formula gives 1.85 m² — the two methods agree within a hundredth, which is why Mosteller became the default.
Two more reference points show how the figure scales:
- 160 cm and 55 kg → √(8,800 ÷ 3,600) = about 1.56 m²
- A child of 110 cm and 20 kg → √(2,200 ÷ 3,600) = about 0.78 m²
Which Formula Produced Your Number?
Because several BSA formulas are in circulation — Mosteller, Du Bois, and others such as Haycock, which is often preferred for infants and children — two calculators can legitimately return slightly different figures for the same person. In the middle of the adult range the disagreement is usually within one or two percent and rarely changes any decision. It grows at the extremes of height and weight, which is why clinical protocols name the formula they expect rather than accepting any BSA value. When you record a result from this calculator, recording the formula alongside it — and your height and weight at the time — makes the figure reproducible later, which is the standard any dosing-adjacent number should meet.
Accuracy Limits and Common Input Errors
BSA formulas are population estimates, and they drift at the extremes. In severe obesity, most formulas overestimate slightly relative to measured surface area; in very muscular or very lean bodies the estimate can sit a few percent off in either direction. For routine clinical use that error is accepted, but it is one reason oncologists sometimes cap or adjust doses rather than applying a formula blindly.
The far bigger source of wrong answers is unit mix-ups. Entering height in inches (69 instead of 175) or weight in pounds (154 instead of 70) produces a BSA that is wildly wrong while still looking like a plausible number — 1.0 or 2.6 m² instead of 1.84. Always confirm the units before trusting the output, and if you work in imperial units, convert first with a dedicated tool. Also note that BSA for children is sometimes calculated with paediatric-specific approaches, and drug dosing in children involves extra safety checks beyond the raw figure.
This calculator provides a general-information estimate of body surface area. It is not a medical measurement and must not be used to set any medication dose; dosing decisions belong to the treating clinical team.
Related Health Measures
BSA is one of several size-based health estimates. The BMI calculator compares weight to height in a simpler index used for weight-category screening, and the body fat calculator estimates composition rather than surface. You can find both, along with the rest of the collection, in the health calculators section. For background reading on the formulas themselves, see the body surface area reference article.