Body Surface Area

How Body Surface Area Is Calculated

Body surface area (BSA) is an estimate of your total skin surface, calculated from height and weight rather than measured directly. It’s used clinically for things that scale better with body size than with weight alone, such as certain medication dosing calculations. Enter your height and weight, and this calculator shows the estimate from three published formulas side by side — plus their average.

The Formulas

Every formula below uses the same two inputs — weight (kg) and height (cm) — so the same two colors track the same two quantities across all three:

DuBois & DuBois (1916) — the oldest and most widely cited BSA formula, still a common clinical default over a century later:

$$\text{BSA} = 0.007184 \times \vA{\text{Weight}}^{0.425} \times \vB{\text{Height}}^{0.725}$$

Mosteller (1987) — a simpler square-root formula that closely approximates DuBois while being easy to compute by hand:

$$\text{BSA} = \sqrt{\frac{\vB{\text{Height}} \times \vA{\text{Weight}}}{3600}}$$

Haycock (1978) — developed using data that included infants and children, so it’s often preferred for pediatric use:

$$\text{BSA} = 0.024265 \times \vA{\text{Weight}}^{0.5378} \times \vB{\text{Height}}^{0.3964}$$

Key Factors to Consider

• The three formulas agree closely for a typical adult body size, but can diverge more at the extremes. For an unusually small or large body size (very low or very high weight relative to height), the formulas’ underlying assumptions can produce noticeably different estimates — another reason clinical dosing always uses a specific, deliberately-chosen formula rather than an average.
• BSA-based dosing exists because some drugs’ effects scale better with body surface than with weight alone. Certain medications, especially chemotherapy agents, have a narrow therapeutic window where getting the dose right matters enormously — BSA is used specifically because research has shown it correlates better with metabolic rate and drug clearance than body weight does for those medications.
• A healthcare provider’s own calculation always takes precedence for any medical decision. Clinical BSA calculations may use a specific formula chosen for the situation, along with precisely measured height and weight taken under controlled conditions — this calculator’s estimate is for general informational purposes only, never a substitute for a real clinical calculation.
• BSA is distinct from BMI, even though both use height and weight. BMI is a screening measure for weight category (underweight, normal, overweight, obese); BSA estimates total body surface area — they answer genuinely different questions and aren’t interchangeable.

Interpreting Your Results

• A small spread between the three formulas is normal, not a sign that something’s wrong. Because the three formulas were derived from different study populations using different statistical methods, they were never going to agree to the decimal place — a spread of a few hundredths of a square meter for a typical adult body size is exactly what you’d expect, not an error in the calculator.
• If you were given a specific BSA figure by a clinician, use that one, not this calculator’s average. A provider’s chosen formula (and precisely measured height and weight) is what any actual dosing calculation is based on — this calculator’s average across three formulas is a general estimate, not a substitute for the specific number a clinical calculation produced.
• A result well outside the “typical adult” range (very low or very high BSA) is exactly where the three formulas diverge the most. If your result sits near an unusual extreme, treat the spread between the three numbers as a signal of genuinely lower confidence in any single figure, rather than picking whichever one happens to be highest or lowest.

Common Mistakes

• Mixing up BSA with BMI. Both use height and weight, but they measure different things — BMI is a weight-category screening tool (underweight/normal/overweight/obese), while BSA estimates total skin surface area in square meters. A calculator result described as “BSA” that looks like a BMI number (a value in the teens to 30s) is likely a different calculation entirely.
• Entering weight and height in the wrong units without noticing. All three formulas here expect metric inputs (kilograms and centimeters) internally — this calculator’s unit toggle converts imperial entries automatically, but manually plugging pounds or inches into one of the raw formulas above without converting first will produce a badly wrong result.
• Treating this estimate as clinically authoritative. This calculator’s result is for general informational purposes — an actual medication dosing decision should always come from a healthcare provider’s own calculation, not a self-service estimate like this one.

Worked Example

A person who is 180 cm (5’11”) tall and weighs 80 kg (176 lb):

1. DuBois: $0.007184 \times \vA{80}^{0.425} \times \vB{180}^{0.725} \approx 1.996 \text{ m}^2$
2. Mosteller: $\sqrt{(\vB{180} \times \vA{80}) \div 3600} = 2.000 \text{ m}^2$
3. Haycock: $0.024265 \times \vA{80}^{0.5378} \times \vB{180}^{0.3964} \approx 2.007 \text{ m}^2$
4. Average: $(1.996 + 2.000 + 2.007) \div 3 \approx 2.001 \text{ m}^2$