Used to index chemo doses and cardiac output. Mosteller formula.
Source: Mosteller, NEJM 1987.
What does body surface area mean?
Body surface area (BSA) is a measure of the total surface area of the human body. Unlike body weight, it scales more proportionally with organ size and function, making it useful for normalising physiological measurements and drug doses across patients of different sizes.
The Mosteller formula, published in the New England Journal of Medicine in 1987, is: BSA (m²) = √(height cm × weight kg ÷ 3600). It was designed to be easy to calculate at the bedside and produces values very close to the older, more complex DuBois formula (1916) while being far simpler to use. Most oncology departments now use Mosteller or the closely similar Haycock formula for paediatric cases.
The reference value of 1.73 m² BSA is embedded in renal physiology, eGFR results are reported per 1.73 m² BSA so that clinicians can compare kidney function across patients of different sizes. Similarly, cardiac index (cardiac output per m² BSA) allows meaningful comparison of heart function between a small adult and a large one.
For chemotherapy, BSA-based dosing has been standard practice for decades, though there is ongoing debate about whether actual body weight (for obese patients) or capped doses produce better outcomes. For the purposes of this calculator, the Mosteller formula is applied directly without modification.
Reference ranges
| Category | Typical BSA (m²) | Notes |
|---|---|---|
| Newborn | 0.25 | Reference for paediatric dosing |
| Child (9 years) | 1.07 | — |
| Average adult woman | 1.6 | — |
| Reference adult (unisex) | 1.73 | GFR / cardiac index baseline |
| Average adult man | 1.9 | — |
| Large adult man | 2.2+ | Above 2.0 m² some protocols cap doses |
When should you see a doctor?
BSA is a clinical calculation rather than a health screening value, so there is no "abnormal" BSA. Its primary use is in medical treatment planning. If you are preparing for chemotherapy or have received a test result indexed to BSA (such as eGFR or cardiac index), your medical team will interpret those values in the context of your complete clinical picture. Do not use this calculator to adjust or question prescribed medication doses without speaking to your oncologist or specialist.
Frequently asked questions
What is body surface area used for?
Body surface area (BSA) is used to normalise or dose a range of clinical measurements. Chemotherapy drugs are often dosed in mg/m² of BSA to account for body size differences. Cardiac output and glomerular filtration rate are frequently indexed to 1.73 m² BSA for comparison between individuals. BSA is preferred over body weight for many drugs because it correlates better with cardiac output and renal clearance.
What is the Mosteller formula for BSA?
The Mosteller formula (1987) calculates BSA as: BSA (m²) = √(height cm × weight kg / 3600). It is the simplest and most commonly used formula in modern clinical practice and gives results very close to the more complex DuBois formula, which was the historical standard.
What is the average BSA for an adult?
The average BSA for adult women is approximately 1.6 m² and for adult men approximately 1.9 m². The commonly used reference value of 1.73 m² represents an average for adults and is used as the normalisation standard for GFR and cardiac index values.