Calculate your BSA using the Du Bois and Mosteller formulas
This calculator is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional.
Body Surface Area (BSA) is a measurement of the total surface area of the human body, expressed in square metres (m²). While it might seem like an obscure metric, BSA plays a critical role in clinical medicine, where it is used to calculate drug dosages (particularly for chemotherapy and other potent medications), assess burn severity, determine cardiac output indices, and normalise physiological measurements such as kidney function (eGFR). The concept of measuring body surface area for medical purposes dates back to the early 20th century. In 1916, Du Bois and Du Bois published their landmark formula based on direct measurements of nine individuals, coating their bodies in moulds to determine actual surface area. Despite its small sample size, the Du Bois formula has stood the test of time and remains the most widely used BSA equation in clinical practice worldwide. The Mosteller formula, published in 1987 in the New England Journal of Medicine, provides a simplified alternative that is easier to calculate mentally and produces results very close to the Du Bois formula. Both formulas are considered clinically acceptable, and the difference between them is typically less than 2%. The average adult body surface area ranges from approximately 1.7 to 2.0 m², with the standard reference value of 1.73 m² used for normalising laboratory values.
To calculate your body surface area: 1. Enter your weight in kilograms. For the most accurate result, weigh yourself in light clothing without shoes. 2. Enter your height in centimetres. 3. Review your results. The calculator displays your BSA using both the Du Bois and Mosteller formulas, along with a classification of whether your BSA falls below average, within the average range, or above average for adults. A clinical note explains how BSA is used in medication dosing. 4. Compare the two formula results using the bar chart. The values should be very similar, typically within 1-2% of each other.
This calculator uses two established BSA formulas: **Du Bois formula (1916) -- most widely used in clinical practice:** BSA (m²) = 0.007184 x height (cm)^0.725 x weight (kg)^0.425 This formula was developed by Delafield Du Bois and Eugene F. Du Bois using direct surface area measurements. The exponents (0.725 for height, 0.425 for weight) reflect the non-linear relationship between body dimensions and surface area. **Mosteller formula (1987) -- simplified alternative:** BSA (m²) = √(height (cm) x weight (kg) / 3600) The Mosteller formula uses a simple square root calculation that can be performed quickly, even by hand. The constant 3600 was derived to match the Du Bois results as closely as possible. **Classification ranges:** - Below average: BSA < 1.7 m² - Average: BSA 1.7 - 2.0 m² - Above average: BSA > 2.0 m² The standard reference BSA of 1.73 m² is used by laboratories worldwide to normalise eGFR (estimated glomerular filtration rate) when assessing kidney function.
BSA has several important clinical applications: **Drug dosing:** Many medications, particularly chemotherapy agents such as carboplatin, cisplatin, and doxorubicin, are dosed based on BSA rather than weight alone. This is because BSA correlates better with blood volume and organ size, providing more consistent drug levels across patients of different sizes. **Burn assessment:** In emergency medicine, BSA is used with the Lund and Browder chart or the Wallace Rule of Nines to estimate the total body surface area affected by burns. This determines fluid resuscitation requirements using the Parkland formula. **Cardiac index:** The cardiac index (cardiac output divided by BSA) normalises cardiac output for body size, allowing meaningful comparison between patients. **Limitations:** The Du Bois formula was developed from a very small sample (9 individuals) and may be less accurate at the extremes of body size (very small children, severely obese adults). Alternative formulas such as Haycock (for paediatric patients) and Boyd may be more appropriate in specific clinical contexts. For clinical decisions, always use the formula specified by your institution's protocols. For more information on BSA in clinical practice, consult the British National Formulary (BNF) or your healthcare provider.