The MedMaths BSA calculator supports four published height-and-weight equations: Mosteller, Du Bois and Du Bois, Haycock, and Gehan & George. They all estimate body surface area in m², but they were derived using different datasets and equations, so the same height and weight can produce slightly different results. This Guide explains those differences and how to handle formula choice safely.
The short answer: follow the formula named by the source you are using
If a medicine reference, treatment protocol, product information, prescriber, pharmacist, or local policy names a specific BSA equation, use that equation. Do not switch to another formula simply because it is easier to calculate or produces a preferred number.
If the source does not specify a formula, do not assume that one equation is a universal default for every clinical use. Mosteller is commonly used because it is simple, but the appropriate choice still depends on the reference, protocol, and local practice you are following.
A current medicine-specific example is caspofungin labelling for pediatric patients: the label explicitly specifies the Mosteller formula, then calculates the dose as BSA × mg/m² and applies a medicine-specific maximum. That is the model to follow: the active source chooses the BSA method and any downstream cap or adjustment.
Why do BSA formulas give different results?
None of these equations directly measures body surface area. Each estimates it from height and weight using constants and mathematical powers derived from a particular dataset. That means small differences are expected even when the same measurements are entered correctly.
For a person who is 170 cm tall and weighs 70 kg, MedMaths returns approximately:
- Mosteller: 1.818 m²
- Du Bois and Du Bois: 1.810 m²
- Haycock: 1.826 m²
- Gehan & George: 1.831 m²
At many typical adult heights and weights the estimates are close. Differences can become more noticeable at body-size extremes, which is another reason to use the equation required by the applicable source rather than changing methods mid-calculation.
The Mosteller formula
Robert D. Mosteller published the simplified square-root equation in 1987. It uses height in centimetres and weight in kilograms and was designed to make BSA easier to calculate. Its simplicity is one reason it is commonly used in modern clinical references and calculators.
Use Mosteller when: the protocol or reference explicitly specifies Mosteller, or when the applicable source otherwise establishes it as the method to use.
The Du Bois and Du Bois formula
Delafield Du Bois and Eugene F. Du Bois published their height-and-weight equation in 1916. It is one of the oldest BSA equations still encountered in clinical literature and was derived from a small historical measurement series.
Use Du Bois when: a protocol, reference, or historical method specifically requires the Du Bois and Du Bois equation.
The Haycock formula
George B. Haycock, George J. Schwartz, and David H. Wisotsky published their equation in 1978. The original study included a broad age range, including infants, children, and adults, which is why the Haycock equation is frequently discussed in paediatric BSA literature.
Use Haycock when: the paediatric or other clinical source you are following specifies Haycock. Its broad validation population does not mean every paediatric medicine should automatically use this formula or BSA-based dosing.
The Gehan & George formula
Edmund A. Gehan and Stephen L. George published their BSA estimation equation in 1970. Like Du Bois and Haycock, it uses separate mathematical powers for height and weight, with its own fitted constant.
Use Gehan & George when: the protocol or reference explicitly names that equation.
Can you swap one BSA formula for another?
Do not assume the formulas are interchangeable for a specific medication or protocol. If a source names an equation, match the calculation to that equation. If it does not, check the current reference or local policy rather than inferring that a different formula is equivalent for that clinical use.
Sources and references
- Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987.
- Du Bois D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. 1916.
- Haycock GB, Schwartz GJ, Wisotsky DH. Geometric method for measuring body surface area. J Pediatr. 1978.
- Gehan EA, George SL. Estimation of human body surface area from height and weight. Cancer Chemother Rep. 1970.
- Fancher KM, et al. Comparison of two different formulas for body surface area in adults at extremes of height and weight. J Oncol Pharm Pract. 2016.
- DailyMed. Caspofungin acetate — Product labeling specifying Mosteller BSA and BSA-based pediatric dosing.
The bottom line
Formula choice is a source-selection question, not a reason to keep recalculating until a preferred BSA appears. Use the equation required by the reference you are following, keep the height and weight units correct, and document the method when it matters to the dose.
When you already know which equation is required, use the MedMaths BSA Calculator to perform the calculation and show the working. If your next question is how an order written in mg/m² becomes the patient's dose in mg, continue to BSA Medication Dosing Explained. For interactive practice, use the BSA dosing lesson.