ReckonBoxHow the body surface area calculator works
Body surface area is an estimate of the total external area of the body, calculated from height and weight and reported in square metres. Enter both and this tool runs every formula it can source at once, then prints the gap between the highest and lowest answer.
That gap is the reason the page exists. BSA is used to dose drugs, and the formula you pick moves the number.
The formulas, and what they disagree about
| Formula | Equation | 175 cm, 70 kg |
|---|---|---|
| Du Bois and Du Bois | 0.007184 x height^0.725 x weight^0.425 | 1.85 |
| Mosteller | square root of (height x weight / 3600) | 1.84 |
| Haycock | 0.024265 x height^0.3964 x weight^0.5378 | 1.85 |
| Gehan and George | 0.0235 x weight^0.51456 x height^0.42246 | 1.85 |
| Fujimoto | 0.008883 x weight^0.444 x height^0.663 | 1.80 |
Height in centimetres, weight in kilograms, result in square metres.
For that mid-range adult the five land within 0.06 m2 of each other, which looks reassuring. It isn't the general case. StatPearls states that BSA values can vary by as much as 0.5 square metres for a standard adult physique depending on which formula is used, and it names what a dosing error causes: myelosuppression or cardiotoxicity.
Push the inputs to the edges of the range and the formulas separate. That's why this tool prints the spread for your own measurements instead of a single confident figure.
Who prints what
calculator.net offers eight formulas and displays every equation. Omni offers five with equations. Neither shows what those choices produce side by side for the same person.
Pearson is the exception, with a compare-all-formulas option, which is the right instinct. Even there the 0.5 m2 figure and its clinical consequence don't appear.
So the field publishes the maths carefully and stays quiet about the disagreement, which is the part a reader would actually want flagged.
Which formula suits whom
Du Bois is the most widely used, and calculator.net notes it has been shown effective for estimating body fat in obese and non-obese patients. StatPearls is less generous: it may overestimate BSA in people with obesity, and may not be accurate for children.
Haycock is described by calculator.net as validated in infants, children and adults, which makes it the paediatric option.
Mosteller earns its place by being simple. Square root of height times weight over 3600 is something you can do on paper at a bedside, and that has kept it in use.
What the number is used for
Drug dosing is the big one, chemotherapy especially. BSA also underpins burn assessment, cardiac index, kidney disease staging and radiation planning. StatPearls frames the appeal plainly: BSA tracks metabolic mass better than weight alone.
The critique lands where the margin is thinnest. Omni notes the objection is strongest for drugs with little room for error, which describes chemotherapy exactly. BSA-based dosing still produces more consistent outcomes than weight-based dosing, so the argument is about refinement, not replacement.
One number worth carrying across: 1.73 m2 is the standard reference adult figure, and it's the same normalisation you see when eGFR is reported per 1.73 square metres. Omni gives 1.9 m2 as an average for men.
What this calculator does not do
BSA capping is absent. Some oncology practice caps BSA for dosing purposes, and no source used to build this page publishes the threshold, so nothing here applies one.
Boyd, Takahira and Schlich appear on calculator.net's list and not here, because the equations weren't available on any page fetched for this build. Five formulas we can print beat eight we can't.
Nothing on this page is a dose. Results are estimates and not medical advice, and a real dose comes from a clinician working to a protocol, usually with the patient in front of them. For the related kidney measure the eGFR calculator uses the same 1.73 m2 normalisation, and the BMI calculator covers the simpler height and weight ratio.
Frequently asked questions
What is body surface area? Body surface area is an estimate of the total external area of the body, expressed in square metres and calculated from height and weight. StatPearls describes it as a better indicator of metabolic mass than weight alone, which is why it is used for drug dosing, chemotherapy calculations, burn assessment, cardiac index and radiation planning.
Which BSA formula should be used? It depends on the population. Du Bois is the most widely used and calculator.net notes it has been shown effective in obese and non-obese patients, though StatPearls cautions it may overestimate BSA in people with obesity and may not be accurate for children. Haycock is described as validated in infants, children and adults. Mosteller survives on being simple enough to compute by hand.
How much do BSA formulas disagree? Enough to matter clinically. StatPearls states that BSA values can vary by as much as 0.5 square metres for a standard adult physique depending on which formula is used, and names myelosuppression and cardiotoxicity as consequences of dosing errors. This calculator prints every formula and the gap between the highest and lowest for your own measurements.
What is the Mosteller formula? Mosteller is the square root of height in centimetres multiplied by weight in kilograms, divided by 3600. For a 175 cm, 70 kg adult that gives 1.84 square metres. Its appeal is that it can be done on paper, which matters at a bedside.
What is the Du Bois formula? Du Bois and Du Bois is 0.007184 times height in centimetres to the power 0.725, times weight in kilograms to the power 0.425. For a 175 cm, 70 kg adult that gives 1.85 square metres, close to Mosteller for a mid-range body and further apart at the extremes.
What is a normal body surface area? Omni gives 1.9 square metres as an average for men, and 1.73 square metres is the standard reference figure for a 70 kg adult. That 1.73 value is the same normalisation used when eGFR is reported per 1.73 square metres.
Should BSA be used for chemotherapy dosing? It is used for it, and the practice has known critics. Omni notes the objection is strongest for drugs with little margin for error, which is exactly the chemotherapy case. Some oncology practice also caps BSA for dosing purposes, and no source used to build this page publishes the threshold, so this calculator does not apply one.
Sources
- StatPearls, body surface area (equations, the 0.5 m2 spread, and dosing consequences)
- calculator.net body surface area calculator (eight published equations)
- Omni Calculator BSA (Gehan and George, Fujimoto, and the reference adult figure)
- Pearson BSA calculator (the one fetched tool offering a compare-all option)