Body Surface Area Calculator
Estimate your body surface area from height and weight using the Mosteller and Du Bois equations.
Example
For a person 170 cm tall weighing 70 kg:
Mosteller = sqrt(170 x 70 / 3600)
= sqrt(11900 / 3600)
= sqrt(3.3056)
= 1.818 m²
Du Bois = 0.007184 x 170^0.725 x 70^0.425
= 1.833 m²Both methods agree closely, giving a BSA of about 1.82 m².
How it works
Enter your height and weight; the tool computes BSA via Mosteller BSA = sqrt(height_cm x weight_kg / 3600) and also shows the Du Bois estimate. Switch units with the metric/imperial toggle.
Good to know
This Body Surface Area (BSA) calculator turns two simple inputs — your height and weight — into an estimate of the total external area of your body, expressed in square meters. It computes the result two ways at once: the Mosteller square-root formula and the older Du Bois power-law formula, then shows their average. You can enter values in metric (cm/kg) or imperial (in/lb), and the toggle converts your numbers automatically. It is aimed at nursing and pharmacy students, clinicians double-checking a figure, and curious people who have seen "BSA" referenced in a dosing chart or lab report.
You would reach for BSA rather than plain weight in situations where physiology scales with surface area instead of mass: estimating chemotherapy and certain other drug doses, indexing cardiac output (cardiac index), or gauging metabolic and fluid needs. Because two formulas are shown side by side, this page is also handy when a protocol specifies one method and you want to confirm you are using the right one.
To read the result, look at the large headline figure (Mosteller, rounded to two decimals) for a quick answer, then use the three-stat row for precision. Mosteller and Du Bois normally land within a few percent of each other; a large gap usually means a typo in the height or weight. The small badge labels the average as below average, typical, or above average for an adult — treat that purely as orientation, not a health verdict. Most adults fall somewhere around 1.6 to 2.0 m².
One practical caveat: BSA formulas were derived mainly from adult and limited pediatric data, so they are estimates, not exact measurements, and accuracy drops at the extremes of body size, in infants, and in people with very high or low body fat. If a number will be used to calculate a real medication dose, verify which formula the protocol requires and have a qualified professional confirm the result before acting on it.
Frequently asked questions
What is the difference between the Mosteller and Du Bois formulas?
Mosteller is a simplified square-root formula (sqrt(height x weight / 3600)) that is easy to compute and widely used for chemotherapy dosing. Du Bois (1916) uses a power-law fit. They usually agree within about 1-3%, and this tool shows both plus their average.
Why is body surface area used instead of body weight?
BSA correlates better with metabolic rate, cardiac output, and renal function than weight alone, so it is often preferred for dosing drugs (especially chemotherapy) and for indexing physiological measurements like cardiac index.
Is my data uploaded anywhere?
No — this calculator runs entirely in your browser; nothing is uploaded.
Is this a substitute for medical advice?
No. These are educational estimates — consult a qualified health professional for medical decisions.
People also ask
What is a normal body surface area for an adult?
Average adult BSA is roughly 1.7 m², with most men around 1.9 m² and most women around 1.6 m². Values typically range from about 1.5 to 2.0 m² depending on height and weight.
How do you calculate BSA using the Mosteller formula?
The Mosteller formula is BSA (m²) = square root of (height in cm × weight in kg ÷ 3600). For example, 170 cm and 70 kg gives the square root of (11900 ÷ 3600), which is about 1.82 m².
Which BSA formula is most accurate?
No single formula is universally most accurate; Mosteller is favored for its simplicity and is common in chemotherapy dosing, while Du Bois has long historical use. They usually agree within a few percent, and accuracy varies with body size and population.
How is BSA used to calculate medication dosage?
For BSA-based dosing, the prescribed dose is given as an amount per square meter (for example, mg/m²) and multiplied by the patient's BSA to get the total dose. This approach is most common in oncology and some pediatric medications.
Can I calculate BSA for a child?
The same Mosteller and Du Bois formulas are sometimes applied to children, but pediatric BSA estimation is less reliable, especially in infants, and clinical settings may use specific pediatric methods. Pediatric dosing decisions should be left to a qualified clinician.
Does BMI tell you the same thing as body surface area?
No. BMI is weight divided by height squared and is used to categorize weight relative to height, while BSA estimates total body surface in square meters. They serve different purposes and are not interchangeable.
Why does BSA correlate with metabolic rate?
Heat loss and many physiological processes scale with surface area rather than mass, so BSA tracks resting metabolic rate, cardiac output, and renal function more closely than weight alone. That is why it is used to index those measurements.
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