Body Surface Area Calculator
Calculate your body surface area (BSA) in square meters from height and weight, using the Mosteller, Du Bois, and Haycock formulas.
Your Measurements
Enter your height and weight, then click Calculate.
How Does the Formula Work?
Body surface area (BSA) is the total external surface of the human body, expressed in square meters (m²). Because BSA tracks metabolic rate and blood volume more closely than weight alone, medicine uses it to scale treatments and measurements to body size. This calculator estimates BSA from height and weight with three published formulas.
Du Bois: BSA = 0.007184 × height^0.725 × weight^0.425
Haycock: BSA = 0.024265 × height^0.3964 × weight^0.5378
Sources: the Mosteller (1987), Du Bois (1916) and Haycock (1978) formulas from the medical literature.
What BSA Is Used For
The most important use is drug dosing. Chemotherapy agents and several other medications are prescribed in milligrams per square meter (mg/m²), because BSA-based dosing reduces the risk of overdosing small patients and underdosing large ones. Burn care uses BSA to express how much of the body is injured (percent of total BSA). Cardiology divides cardiac output by BSA to obtain the cardiac index, allowing hearts of different-sized people to be compared. Nephrology normalizes kidney function the same way: glomerular filtration rate (GFR) is conventionally reported per 1.73 m², the historical average adult BSA. Physiologists also use BSA to compare basal metabolic rates across body sizes.
Why the Formulas Differ
Direct measurement of body surface is impractical, so all BSA formulas are statistical fits to small measured samples. Du Bois and Du Bois (1916) derived their exponents from just 9 subjects, yet the formula became the research standard for a century. Haycock and colleagues (1978) fitted 81 subjects from premature infants to adults, which is why their formula is often preferred in pediatrics. Mosteller (1987) simplified the math to a single square root that can be computed at the bedside; large comparisons show it agrees with the older formulas within a few percent for typical adults, and it is now the common clinical default.
Methodology
This tool uses the clinical standard Mosteller formula as the primary result. Du Bois (the classic 1916 reference) and Haycock (often preferred for children) are shown alongside for comparison. Imperial inputs are converted with exact definitions: 1 inch = 2.54 cm and 1 pound = 0.453592 kg. Results are estimates; individual body composition is not taken into account.
Typical Values
The average adult BSA is about 1.7 m² overall, with men averaging roughly 1.9 m² and women roughly 1.6 m². A newborn has a BSA of about 0.25 m², a 2-year-old about 0.5 m², and a 10-year-old about 1.14 m². These reference points are useful for a quick sanity check of any calculated value.
Tips & Recommendations
Mosteller is the practical clinical default. Du Bois is common in older research and reference tables. Haycock was fitted across infants to adults and is often preferred in pediatrics.
The three formulas typically agree within 2 to 3 percent for adults. A difference in the second decimal place is expected, not an error.
BSA is used to dose chemotherapy and other drugs, but that calculation belongs to your medical team. Always consult a doctor; this tool is an estimate only.
Typical adults fall between about 1.4 and 2.2 m². If your result is far outside this range, double-check your units and inputs.
Frequently Asked Questions
What is body surface area?
Body surface area (BSA) is the total external surface of the human body, measured in square meters. Unlike weight alone, BSA correlates closely with metabolic rate and blood volume, which is why medicine uses it to scale drug doses and physiological measurements to body size.
Which BSA formula is the most accurate?
No single formula is universally best. The Mosteller formula is the modern clinical standard because it is simple and matches other formulas within a few percent. Du Bois is the classic 1916 reference used in older research, and Haycock performs well in children and small patients. For typical adults the three agree within about 2 to 3 percent.
What is BSA used for?
BSA is used to dose chemotherapy and other drugs (mg per m²), to assess burn extent, to calculate the cardiac index (cardiac output divided by BSA), to normalize glomerular filtration rate (GFR is reported per 1.73 m²), and to compare metabolic rates between people of different sizes.
What is the average BSA?
The average adult BSA is about 1.7 m² overall: roughly 1.9 m² for men and 1.6 m² for women. Newborns start around 0.25 m² and a 10-year-old child averages about 1.14 m². Values vary widely with height and weight.
What is the difference between Mosteller and Du Bois?
Both estimate the same quantity from height and weight but with different math. Mosteller (1987) uses a simple square root, which made it practical for bedside use. Du Bois (1916) uses power exponents fitted to direct body measurements of 9 subjects. For most adults the results differ by less than 2 percent.
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