Body Surface Area Calculator
Calculate body surface area in m² by the Du Bois, Mosteller, Haycock and Gehan formulas at once, with the drug dose that BSA implies.
Body Surface Area Calculator: with the default inputs, body surface area is 1.95 m².
All four are computed; this one becomes the headline number.
- Mosteller
- 1.952 m²
- Du Bois & Du Bois
- 1.948 m²
- Haycock
- 1.958 m²
- Gehan & George
- 1.962 m²
- Spread across the four formulas
- 0.7%Range ÷ mean. Typically 2–4% in adults, larger at the extremes of size.
- Dose at this BSA
- 0Milligrams, from the dose per m² you entered.
- BSA per kg
- 0.0253m² per kilogram — falls as body size rises, which is why BSA dosing exists.
Assumptions
- All four equations take height in centimetres and weight in kilograms and return square metres.
- They are regression fits to small samples of directly measured subjects and are least reliable at the extremes of body size.
- The optional dose is a plain multiplication — no caps, banding, rounding or organ-function adjustment.
- BSA describes geometry, not body composition; it cannot distinguish lean from fat mass.
| Formula | Published | BSA(m²) | vs. Mosteller |
|---|---|---|---|
| Mosteller | Mosteller (1987) | 1.952 m² | 0% |
| Du Bois & Du Bois | Du Bois & Du Bois (1916) | 1.948 m² | -0.18% |
| Haycock | Haycock, Schwartz & Wisotsky (1978) | 1.958 m² | 0.32% |
| Gehan & George | Gehan & George (1970) | 1.962 m² | 0.52% |
In average-sized adults the four agree within a few percent. They diverge at very low and very high body weights, where the original measured samples were thin.
How this is worked out
The formula
Height H in centimetres, weight W in kilograms, BSA in m² Mosteller (1987): BSA = √(H × W ÷ 3600) Du Bois & Du Bois (1916): BSA = 0.007184 × W^0.425 × H^0.725 Haycock et al. (1978): BSA = 0.024265 × H^0.3964 × W^0.5378 Gehan & George (1970): BSA = 0.0235 × H^0.42246 × W^0.51456
Open How it’s calculated above to see this worked through with your own numbers.
What you enter
- Height
- A number.in in, cm, m · from 20 to 100 · defaults to 70
- Weight
- A number.in lb, kg, st · from 5 to 700 · defaults to 170
- Headline formula
- All four are computed; this one becomes the headline number.Mosteller (1987) — the clinical default · Du Bois & Du Bois (1916) — the original · Haycock (1978) — validated in children · Gehan & George (1970)
- Drug dose per m²(under More options)
- Optional. Multiplies the BSA to give a total dose. Leave at 0 to skip.from 0 to 100000 · defaults to 0
What you get back
- Body surface areamain answer
- Mosteller
- Du Bois & Du Bois
- Haycock
- Gehan & George
- Spread across the four formulas
- Range ÷ mean. Typically 2–4% in adults, larger at the extremes of size.
- Dose at this BSA
- Milligrams, from the dose per m² you entered.
- BSA per kg
- m² per kilogram — falls as body size rises, which is why BSA dosing exists.
What this assumes
- All four equations take height in centimetres and weight in kilograms and return square metres.
- They are regression fits to small samples of directly measured subjects and are least reliable at the extremes of body size.
- The optional dose is a plain multiplication — no caps, banding, rounding or organ-function adjustment.
- BSA describes geometry, not body composition; it cannot distinguish lean from fat mass.
About this calculator
Body surface area is the standard scaling variable in clinical pharmacology. Cardiac output, glomerular filtration rate, and the doses of most cytotoxic chemotherapy agents are all expressed per square metre, because metabolic rate and organ size track surface area far better than they track body weight. A typical adult is somewhere between 1.6 and 2.1 m².
The formulas
Nobody measures body surface area directly any more. The original work did: Du Bois and Du Bois in 1916 wrapped nine subjects in paper moulds, cut them into flat pieces and measured the area, then fitted a power law to height and weight. Their equation is still in use over a century later.
Mosteller published the simplification in a 1987 letter to the New England Journal of Medicine: the square root of height times weight over 3,600. It agrees with Du Bois within a couple of percent across the normal adult range, it can be done on any calculator, and it has become the clinical default for that reason. A 180 cm, 80 kg adult is exactly 2.0 m² — √(180 × 80 ÷ 3600) = √4.
Haycock (1978) was fitted with children included in the sample and is the formula of choice in paediatrics, where Du Bois tends to under-read. Gehan and George (1970) refitted the Du Bois form on a much larger sample of directly measured subjects.
Enter your height and weight and all four are shown at once, along with how far apart they are. In an average adult the spread is typically 2–4%; at the extremes of body size it widens considerably, because every formula was fitted on a small number of directly measured people who were mostly of ordinary size.
Why doses use BSA
Drug clearance depends on liver and kidney function, which scale with metabolic rate, which scales roughly with surface area rather than mass. A 120 kg adult is twice the weight of a 60 kg adult but only about 1.4 times the surface area — so a per-kilogram dose would substantially overdose the larger patient for a drug with a narrow therapeutic window. That is the whole justification for mg/m² dosing, and it is why BSA remains standard in oncology despite well-known limitations.
Those limitations are real. BSA does not account for body composition, so a patient with a large fat mass gets a dose based on surface area that their lean tissue is doing the metabolising for. Many protocols therefore cap BSA at 2.0 or 2.2 m², dose on adjusted or ideal body weight, or use direct pharmacokinetic targets such as carboplatin's Calvert formula instead.
Using the dose field
Under More options, entering a dose in mg/m² multiplies it by the headline BSA. It is a convenience for reading a protocol, not a prescribing tool: rounding rules, dose caps, dose banding, renal and hepatic adjustments and prior-toxicity reductions all sit on top and belong with the prescriber and pharmacist.
Frequently asked questions
▸What is the Mosteller formula for BSA?
BSA in m² = the square root of (height in cm × weight in kg ÷ 3600). For 180 cm and 80 kg that is √4 = exactly 2.0 m².
▸Which BSA formula should I use?
Mosteller is the clinical default for adults because it is simple and agrees closely with Du Bois. Haycock is preferred in paediatrics. For a given protocol, use whichever formula the protocol specifies.
▸What is a normal body surface area?
Roughly 1.6 to 1.9 m² for adult women and 1.8 to 2.1 m² for adult men. Newborns are near 0.25 m², and a ten-year-old around 1.1 m².
▸Why are chemotherapy doses based on BSA?
Drug clearance follows metabolic rate, which scales with surface area more closely than with body weight. Dosing per kilogram would overdose larger patients for drugs with a narrow therapeutic window.
▸Do the formulas disagree?
By a few percent in average-sized adults, and by more at very low or very high body weight, where the original directly-measured samples were sparse. The table shows the spread for your figures.
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