What body surface area is
Body surface area (BSA) is an estimate of the total outer area of your body, given in square meters. It tracks overall body size better than weight on its own, which is why medicine uses it to scale things that depend on how big a person is. A typical adult sits near 1.7 m².
You cannot measure skin area directly in a clinic, so it is estimated from height and weight with a validated formula. Several exist, and they agree closely for most adults. This calculator runs the three that appear most often in dosing references.
The three formulas
The sources are Mosteller RD (1987, New England Journal of Medicine), Du Bois D and Du Bois EF (1916), and Haycock GB and colleagues (1978). Each returns an area in square meters.
- Mosteller: BSA = √(height[cm] × weight[kg] ÷ 3600)
- Du Bois: BSA = 0.007184 × height[cm]^0.725 × weight[kg]^0.425
- Haycock: BSA = 0.024265 × height[cm]^0.3964 × weight[kg]^0.5378
Worked example: at 180 cm and 80 kg, Mosteller gives √(180 × 80 ÷ 3600) = √4 = 2.00 m². Du Bois and Haycock return about 2.00 and 2.01 m² for the same person, so the three agree to within a rounding step. Mosteller is the headline here because it is the one most protocols use.
Why it is used for dosing
Many drugs, chemotherapy in particular, are prescribed as a dose per square meter of body surface area. Fluid and nutrition rates in intensive care are sometimes set the same way. BSA is used because it lines up with metabolic rate and organ size better than body weight, so it spreads a dose more evenly across people of different builds.
What it is not
BSA is a clinical input, not a fitness or health score. It says nothing about body fat, muscle, or weight status, and a higher figure is not better or worse. This tool is an estimate for general understanding and is not medical advice; any real dose belongs to a clinician working from measured values. For everyday goals, a weight-status check from the BMI calculator or a target range from the ideal weight calculator is the more useful number.
