Body Surface Area (BSA) Calculator

What is a body surface area calculator?

A body surface area (BSA) calculator estimates the total external area of the human body, expressed in square meters, from just two measurements: height and weight. BSA is a more representative measure of metabolic mass than body weight alone, because it is less affected by abnormal adipose tissue. For that reason, clinicians often prefer it when they need a number that scales with the size of a person’s metabolically active surface.

The calculator above lets you choose between two widely used estimation formulas, the Du Bois and the Mosteller, and accepts height and weight in both metric and imperial units.

Why body surface area matters

Body surface area is used across medicine and physiology whenever a quantity needs to be scaled to body size in a way that height or weight alone cannot capture. Common applications include:

• Drug dosing: Many medications, especially chemotherapy agents, are dosed per square meter of BSA rather than per kilogram of body weight.
• Cardiac index: Cardiac output is normalized by BSA to compare heart performance across people of different sizes.
• Burn assessment: The proportion of skin affected by burns is judged against total body surface area.
• Renal function: Glomerular filtration rate is frequently standardized to a reference BSA of 1.73 m².

Because these uses can influence clinical decisions, several formulas have been developed to estimate BSA without the impractical task of measuring it directly.

How does the calculator work?

You enter your height and weight, pick a formula, and the calculator returns your estimated body surface area in square meters. Internally, height is converted to centimeters and weight to kilograms before the chosen formula is applied, so you can mix units freely.

Du Bois formula

Published by Du Bois and Du Bois in 1916, this is the classic and most cited BSA equation:

$BSA = 0.007184 \times W^{0.425} \times H^{0.725}$

where $W$ is weight in kilograms and $H$ is height in centimeters.

Mosteller formula

Introduced by Mosteller in 1987, this formula is popular because it is simple enough to compute by hand:

$BSA = \sqrt{\frac{H \times W}{3600}}$

where $H$ is height in centimeters and $W$ is weight in kilograms. The two formulas usually agree to within a few percent for adults of average build.

Worked examples

1. Adult, 180 cm tall, weighing 70 kg (Du Bois): $BSA = 0.007184 \times 70^{0.425} \times 180^{0.725} \approx 1.89 \ \text{m}^2$

2. Same person with the Mosteller formula: $BSA = \sqrt{\frac{180 \times 70}{3600}} = \sqrt{3.5} \approx 1.87 \ \text{m}^2$

3. Larger adult, 175 cm tall, weighing 85 kg (Du Bois): $BSA = 0.007184 \times 85^{0.425} \times 175^{0.725} \approx 2.01 \ \text{m}^2$

The small difference between the Du Bois and Mosteller results in the first two examples is typical and rarely changes clinical decisions.

Typical values

For reference, the average BSA of an adult is roughly 1.7 m². Common approximate ranges are about 1.6 m² for an adult woman, 1.9 m² for an adult man, and 1.07 m² for a 9-year-old child. Your own value depends on your exact height and weight, which is why an individual calculation is more reliable than a rule of thumb.

Practical notes

• BSA formulas are estimates derived from measurements of small groups of people, so they are most accurate for adults of average proportions and less precise at the extremes of body size.
• For infants and small children, specialized pediatric considerations apply; consult a clinician for medical dosing decisions.
• A BSA value should never replace professional medical advice. Use this calculator for educational and informational purposes.

To explore other body metrics, try the BMI calculator, the body fat calculator, or the ideal weight calculator.

FAQs

Which BSA formula should I use?

The Du Bois formula is the historical standard and the one most often referenced in the literature. The Mosteller formula is easier to calculate and gives very similar results, which is why it is widely used in clinical practice. For most adults the choice makes little practical difference.

What units does the calculator use?

Body surface area is reported in square meters (m²). You can enter height in centimeters, meters, inches, or feet, and weight in kilograms or pounds; the calculator converts everything internally.

Is BSA the same as BMI?

No. Body mass index relates weight to height as a measure of relative body fatness, while body surface area estimates the actual area of your skin. They answer different questions and are used for different purposes.

Why is BSA used for medication dosing?

Body surface area correlates well with several physiological processes, including blood volume and metabolic rate, that influence how the body handles drugs. Dosing per square meter therefore helps tailor doses to body size more reliably than weight alone in many cases.