Body Surface Area Calculator
Calculate your body surface area with eight published formulas, side by side.
Body Surface Area Calculator — your inputs
- Sex
- Male
- Height
- 175 cm
- Weight
- 70 kg
- Unit system
- Metric
Key takeaways
- Body surface area is the external area of the body in square metres — around 1.7 m² for an average adult woman and 1.9 m² for an average adult man.
- It is used to dose medicines that scale with the whole body rather than with weight. Most chemotherapy is prescribed per square metre.5
- Mosteller is the clinical default: a single square root, simple enough to verify by hand, which is a genuine safety property when a dose depends on it.2
- No formula measures anything. Du Bois fitted his to nine subjects in 1916, and it is still in daily use.1
- The 1.73 m² in every eGFR result is a standard body, not yours — which is why this number and your kidney result belong together.
How to use this calculator
Enter your height and weight in either unit system.
The headline figure uses Mosteller, which is what most clinical services use.
The table shows all eight formulas so you can see how much the choice actually changes the answer for your measurements.
Understanding your result
Body surface area is the external area of the body in square metres. It is used to dose medicines that scale with the whole body rather than with weight — most chemotherapy is prescribed per square metre — and to index cardiac output.
It is also the quantity hiding in every eGFR result: the 1.73 m² in mL/min/1.73m² is a standard adult body, and your own figure tells you how far your kidneys' reported rate has been scaled from the real one.
No formula measures anything directly. Each was fitted to a small number of subjects — Du Bois used nine — so agreement in the middle of the range and divergence at the extremes is expected, and is exactly what the comparison table shows.
Why anyone needs this number
Body surface area is an odd quantity to want. Nobody measures their own, it does not appear on a health check, and it has no target value. It matters because several things in medicine scale with it better than they scale with weight — basal metabolic rate, blood volume, cardiac output, and the renal clearance of many drugs.
- Chemotherapy dosing. Most cytotoxic drugs are prescribed in mg per m². The practice dates to the 1950s, when BSA was found to translate animal doses to humans more reliably than weight.5
- Cardiac index. Cardiac output divided by BSA, so that a large and a small person can be compared on the same scale.
- Burn assessment. The proportion of body surface affected drives fluid resuscitation.
- Kidney function. eGFR is reported per 1.73 m², so knowing your own BSA tells you how far the reported figure has been scaled from your actual filtration rate.
The eight formulas
| Formula | Equation | Year |
|---|---|---|
| Du Bois & Du Bois | 0.007184 × W^0.425 × H^0.725 | 1916 |
| Takahira | 0.007241 × W^0.425 × H^0.725 | 1925 |
| Boyd | 0.0003207 × H^0.3 × Wg^(0.7285 − 0.0188 × log₁₀Wg) | 1935 |
| Fujimoto | 0.008883 × H^0.663 × W^0.444 | 1968 |
| Gehan & George | 0.0235 × H^0.42246 × W^0.51456 | 1970 |
| Haycock | 0.024265 × H^0.3964 × W^0.5378 | 1978 |
| Mosteller | √(H × W / 3600) | 1987 |
| Schlich | Sex-specific; see the result table | 2010 |
They differ because each was fitted to a different, small sample using a different method. Du Bois and Du Bois wrapped subjects in paper moulds and measured the flattened area. Others coated subjects in a measurable material, or approximated the body as a set of geometric solids. Takahira's is Du Bois with one coefficient adjusted for a Japanese population; Fujimoto's was fitted to a Japanese sample outright.
How much does the choice matter?
For an average-sized adult, very little — the formulas typically fall within 2–3% of each other. The spread widens at the extremes of height and weight, which is exactly where the original samples ran out of data. That is why this page shows the range alongside the headline figure.
Why Mosteller became the default
Mosteller published his formula in 1987 as a single paragraph in a letter to the New England Journal of Medicine.2 It is not more accurate than Du Bois; it agrees with it closely across normal adult sizes. Its advantage is that it is a square root of one product, computable on any calculator and checkable in your head to within a decimal place.
That matters more than it sounds. When a chemotherapy dose depends on the number, a formula that a pharmacist can sanity-check without a computer is a formula that catches transcription errors. Simplicity is a safety property, not merely a convenience.
The long-standing argument about BSA dosing
Dosing chemotherapy per square metre has been questioned for as long as it has been practised. The rationale — that BSA correlates with the physiological variables governing drug handling — holds only loosely for many individual drugs, and reviews have repeatedly found that BSA-based dosing does not meaningfully reduce the variability in drug exposure between patients.5
It persists because the alternatives are worse in practice: flat dosing ignores real size differences, and individualised pharmacokinetic dosing requires blood sampling that most services cannot run at scale. For a handful of agents — carboplatin is the standard example — dosing is calculated from kidney function instead, which is a better fit for how that drug is actually cleared.
This is not a dosing tool
Real chemotherapy dosing accounts for organ function, prior toxicity, performance status, and protocol-specific caps that often limit the calculated dose. Never use a number from this page to check or question a prescribed dose without speaking to the team that wrote it.
Terms used on this page
- Cardiac index
- Cardiac output divided by body surface area, in litres per minute per m². Indexing to BSA is what lets the heart function of a 50 kg and a 100 kg person be compared on the same scale.
- Normalisation
- Expressing a measurement per unit of body size so that people of different sizes can be compared. eGFR is normalised to 1.73 m²; cardiac index is normalised to your own BSA.
- Allometric scaling
- The observation that biological quantities scale with body mass raised to a power rather than in direct proportion — which is why every BSA formula uses fractional exponents rather than simple multiplication.
The formula
- Height 180 cm, weight 70 kg
- Mosteller: √(180 × 70 / 3600) = √3.5
Source: Mosteller, Du Bois and six more. Published clinical/scientific formula.
Limitations
- Every formula is an estimate from height and weight — none of them measures surface area, and none can see body shape or composition.
- The original datasets were small and not diverse; accuracy is weakest at the extremes of size, in children, and in people with obesity.
- BSA-based chemotherapy dosing is a clinical decision made by an oncology team, who account for organ function, prior toxicity and dose caps. This calculator does not.
- Two formulas can differ by more than 5% for the same person, which is why the range matters as much as the headline.
References
- 1.A formula to estimate the approximate surface area if height and weight be known. Du Bois & Du Bois, Archives of Internal Medicine 17:863–871, 1916.
- 2.Simplified calculation of body-surface area. Mosteller, R.D., New England Journal of Medicine 317(17):1098, 1987.
- 3.Geometric method for measuring body surface area: a height-weight formula validated in infants, children, and adults. Haycock et al., Journal of Pediatrics 93(1):62–66, 1978.
- 4.Estimation of human body surface area from height and weight. Gehan & George, Cancer Chemotherapy Reports 54(4):225–235, 1970.
- 5.Body surface area as a determinant of pharmacokinetics and drug dosing. Sacco et al., Investigational New Drugs 28(5):531–546, 2010.
Frequently asked questions
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Open calculatorNot medical advice. This calculator is for general informational purposes only and is not a substitute for professional medical guidance. Always consult a qualified healthcare provider before making decisions about your health. Read the full medical disclaimer.
Printed from mystatura.com — for general information only, not medical advice.