CalcPro

Body Surface Area Calculator

Body surface area (BSA) via the Mosteller formula.

Not medical advice. This tool is for general information and education only. It is not a diagnosis and cannot replace a doctor. Consult a qualified healthcare professional before acting on any result.

How it works

The Mosteller formula calculates your body surface area by combining your height and weight into a single measurement. This approach is preferred in clinical settings because it reflects how physiological processes—like metabolism and drug clearance—actually scale with body size. Unlike weight alone, BSA accounts for the fact that a tall person and a heavy person may need different medication doses even at the same weight.

You simply enter your height and weight (in either metric or US units), and the calculator converts them if needed, then applies the formula to give you your BSA in square meters.

The formula

BSA (m²) = √(Height (cm) × Weight (kg) / 3600)

Worked example

Let's calculate the BSA for a person who is 175 cm tall and weighs 70 kg.

Step 1: Multiply height by weight
175 × 70 = 12,250

Step 2: Divide by 3,600
12,250 ÷ 3,600 = 3.403

Step 3: Take the square root
√3.403 = 1.845 m²

This person's body surface area is 1.85 m², which falls in the typical adult range.

If using US units: Suppose someone is 5'9" (69 inches) and weighs 154 lb. First, convert:

  • 69 inches × 2.54 = 175.3 cm
  • 154 lb ÷ 2.205 = 69.8 kg

Then apply the formula as above to get approximately 1.84 m².

Common mistakes

Unit confusion: The formula always requires centimeters and kilograms. If you enter pounds or inches, make sure the calculator converts them first—or do it yourself (1 inch = 2.54 cm; 1 lb = 0.4536 kg). Forgetting this step will give a nonsensical result.

Rounding too early: Keep at least two decimal places through each step, especially when taking the square root. Rounding 3.403 to 3.4 before the square root introduces error.

Assuming one formula fits all: While Mosteller is standard, some settings use DuBois, Boyd, or other formulas. If your doctor mentions a different BSA value, they may be using another equation. Don't assume an error; ask which formula they used.

Forgetting this is an estimate, not medical advice. This calculator is a tool for reference and education only. Drug dosing, burn assessment, and other clinical decisions must always be made by a qualified healthcare provider who considers your full medical history, kidney and liver function, and other factors beyond BSA alone.

Recalculate your BSA if your weight or height changes significantly, and always verify the result with your doctor before it affects any treatment decision.

Frequently asked questions

What is body surface area and why does it matter?

Body surface area (BSA) is the total area of your skin exposed to the environment, measured in square meters (m²). It's used in medicine to calculate drug dosages, assess burn severity, and evaluate kidney function. BSA is more accurate than weight alone for dosing because it accounts for how body size actually scales.

What is the Mosteller formula?

The Mosteller formula is: BSA (m²) = √(Height (cm) × Weight (kg) / 3600). It's one of the most widely used BSA equations in clinical practice because it's simple, reliable, and works well across different ages and body types.

Can I use this for medication dosing?

This calculator provides an estimate only and is not professional medical advice. Always consult your doctor or pharmacist before adjusting any medication dose. They will verify your BSA calculation and account for other health factors.

Does BSA change over time?

Yes. BSA increases as children grow and can change in adults with significant weight gain or loss. If your weight or height changes substantially, recalculate your BSA, especially if it affects medical treatment decisions.

How accurate is the Mosteller formula?

The Mosteller formula is highly accurate for most people and is preferred by many hospitals and clinics. However, it may be less precise for very obese individuals or those with unusual body proportions. Your healthcare provider may use alternative formulas if needed.

What's a normal BSA range?

Average BSA for adults is 1.5–2.0 m². Children have smaller BSAs (0.5–1.5 m²) depending on age and size. Very tall or heavy individuals may exceed 2.5 m². Your result should always be interpreted by a healthcare professional in context.

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