BSA Calculator

What Is Body Surface Area?

Body surface area (BSA) estimates the total area of your skin in square meters. It is widely used in medicine for calculating drug dosages, burn treatment plans, fluid resuscitation, and cardiac index measurements. BSA-based dosing is the standard for chemotherapy and many IV medications because it accounts for body size more precisely than weight alone. This calculator estimates your BSA using the Du Bois, Mosteller, and Haycock formulas.

Common BSA Formulas

The Du Bois formula (1916) is the oldest and most referenced: BSA = 0.007184 × height(cm)^0.725 × weight(kg)^0.425. The Mosteller formula is simpler and equally accurate for most adults: BSA = square root of (height(cm) × weight(kg) / 3600). The Haycock formula is preferred for pediatric patients. For an average adult male at 70 kg and 170 cm, BSA is approximately 1.8 m². For an average adult female at 60 kg and 160 cm, BSA is about 1.6 m². The average adult BSA range is 1.5 to 2.2 m².

Clinical Applications

Chemotherapy doses are almost always calculated per m² of BSA to account for differences in drug metabolism across body sizes. A standard dose might be listed as 75 mg/m², meaning a patient with a BSA of 1.9 m² receives 142.5 mg. Burn severity is assessed as a percentage of total BSA, and the rule of nines divides the body into sections of 9% or 18% each. Cardiac index (cardiac output divided by BSA) uses body surface area to normalize heart function measurements across patients of different sizes.

BSA by Height and Weight: Reference Values

The values below use the Mosteller formula, the version most hospitals use because it is easy to compute at the bedside. Enter your own height and weight in the calculator above for an exact figure across all three formulas.

DuBois and Mosteller agree closely for adults: a 170 cm, 70 kg adult comes out at 1.81 m² by DuBois and 1.82 m² by Mosteller. The formulas diverge more at the extremes of size, which is why pediatric dosing often uses Haycock instead.

Why BSA Instead of Weight for Drug Dosing?

Body surface area tracks metabolic rate, blood volume, and organ size better than weight alone. Two people can weigh the same while carrying very different amounts of muscle and fat, and their bodies clear drugs at different rates. Dosing per square meter narrows that gap. It matters most for drugs with a narrow therapeutic window, where a dose slightly too high is toxic and slightly too low does nothing: chemotherapy agents are the clearest case. A dose written as 75 mg/m² gives a 1.9 m² patient 142.5 mg and a 1.6 m² patient 120 mg, matching the drug to the person rather than to a flat number.

BSA vs BMI

BMI measures weight relative to height as a health screening tool. BSA measures physical surface area for clinical dosing and treatment calculations. They serve completely different purposes. A high BMI may indicate excess weight, while BSA simply describes how large you are physically. Both use height and weight as inputs but apply them in different formulas with different clinical applications.

Frequently asked questions