Body Surface Area Calculator
Calculate body surface area with Du Bois, Mosteller and six other published equations.
Your measurements
BSA is used to scale chemotherapy doses, cardiac index and burn assessment. This calculator is a reference for checking a figure, not a substitute for the dosing protocol in use. Never adjust medication from a number on a web page.
This calculates body surface area in square metres from height and weight, using the Mosteller and Du Bois formulas.
BSA is used clinically for drug dosing and for indexing physiological measurements. It is not a fitness or body composition measure.
What body surface area is used for
Body surface area is the total external area of the body, in square metres. A 70 kg adult of 175 cm has a BSA of about 1.84 m².
It is used clinically rather than personally. Chemotherapy dosing is the best-known application, along with indexing cardiac output, calculating fluid requirements for burns, and estimating renal function.
The reason BSA is preferred over body weight for some drugs is that it correlates better with metabolic rate and blood volume than weight alone. Two people at 70 kg but very different heights have different surface areas and different physiological scaling, and weight-based dosing would treat them identically.
The formulas agree closely for typical adults. Mosteller is preferred in practice simply because it is easy to compute and remember.
What to enter
- Height
- In centimetres. Inches × 2.54 converts.
- Weight
- In kilograms. Pounds ÷ 2.205 converts.
- Formula
- Mosteller is the practical default. Du Bois is the older standard and gives very similar answers for adults.
The formulas and where BSA is used
- Mosteller (1987)
- √(height cm × weight kg ÷ 3600). Simple enough to do mentally, and the most widely used.
- Du Bois (1916)
- 0.007184 × kg^0.425 × cm^0.725. The original standard, still cited in older literature.
- Haycock and Gehan-George
- Alternatives, generally preferred for children and infants.
- Chemotherapy dosing
- Most cytotoxic agents are dosed in mg/m², which is the main reason BSA is calculated.
- Cardiac index
- Cardiac output divided by BSA, allowing comparison between people of different sizes.
What this assumes
These formulas estimate surface area from height and weight. They do not measure it, and they were derived from small samples by modern standards.
Accuracy is poorer at the extremes of body size, particularly in severe obesity, which is a known limitation in oncology dosing.
How to calculate your body surface area
Mosteller is one square root, which is why it displaced the older formulas in practice.
- height
- In centimetres
- weight
- In kilograms
- 3600
- The constant that produces square metres
Convert to metric. Inches × 2.54 for centimetres; pounds ÷ 2.205 for kilograms.
Multiply height by weight. 175 × 70 = 12,250.
Divide by 3,600. 12,250 ÷ 3,600 = 3.403.
Take the square root. √3.403 = 1.84 m².
See a worked example: two adults of different sizes
- Adult A
- 70 kg, 175 cm
- Adult B
- 50 kg, 160 cm
A, Mosteller: √(175 × 70 ÷ 3600) = √3.403 = 1.84 m². Du Bois gives 1.85 m², essentially the same.
B, Mosteller: √(160 × 50 ÷ 3600) = 1.49 m².
A is 40% heavier than B but only 23% larger by surface area, because BSA scales sub-linearly with weight.
That is exactly why some drugs are dosed by BSA rather than weight: weight-based dosing would over-dose the larger patient.
1.84 m² and 1.49 m²
Frequently asked questions
- What is body surface area used for?
Mainly clinical calculations. Chemotherapy dosing in mg/m² is the most common, along with indexing cardiac output, fluid resuscitation in burns, and some renal measurements.
It is not a health or fitness measure. If you are looking at body composition, body fat percentage or waist measurements are the relevant figures.
- Which formula should I use?
Mosteller for adults. It is simple, widely adopted, and agrees closely with the older Du Bois formula for typical body sizes.
For children and infants, Haycock or Gehan-George are generally preferred, since the adult formulas were not derived from paediatric data.
- Why are chemotherapy doses based on BSA?
Because BSA correlates better with metabolic rate, blood volume and drug clearance than body weight alone, so it scales dose more appropriately across body sizes.
The practice does have known limitations, particularly at the extremes of body size, and dosing decisions are made by clinicians with much more information than a formula. Never adjust a prescribed dose based on a calculator.
- How accurate are these formulas?
For typical adults they agree with each other closely and with measured values reasonably well. Du Bois was derived from a very small sample by modern standards, and Mosteller was fitted to reproduce it more simply.
Accuracy falls at the extremes, especially in severe obesity, which is a recognised issue in oncology and why capping or adjusting doses is sometimes discussed.
- What is a normal BSA?
Roughly 1.6-2.0 m² for adults, varying with height and weight. About 1.9 m² for an average adult man and 1.6 m² for an average adult woman.
There is no healthy or unhealthy BSA. It is a scaling factor, not an assessment.
- How does BSA relate to eGFR?
Standard eGFR is reported normalised to a BSA of 1.73 m², which lets results be compared between people of different sizes.
For drug dosing in patients of unusual size, clinicians sometimes de-normalise it back to absolute clearance using actual BSA. That is a clinical calculation, not a self-assessment.
Problems people actually run into
Using BSA as a body composition measure
BSA has no healthy range and says nothing about fat, muscle or fitness. It is a scaling factor for clinical calculations.
For body composition, use body fat percentage or waist circumference. BSA will tell you nothing useful about health.
Recalculating a prescribed dose
Clinical dosing accounts for organ function, other medications, prior toxicity and institutional protocols. A BSA figure is one input among many.
If a dose looks inconsistent with a calculated BSA, raise it with the prescribing team rather than acting on it. There are usually good reasons for the difference.
Results are estimates for general information only and are not professional financial, medical, or legal advice. Read our full disclaimer.
Sources
- Mosteller, Simplified calculation of body-surface area, N Engl J Med 1987;317:1098 · National Library of Medicine (PubMed)
Last updated: September 13, 2026
