Body Surface Area Calculator

Body surface area (BSA) is the measured or calculated surface area of a human body, typically expressed in square meters (m²). Unlike BMI which relates weight to height, BSA provides the actual external surface area. It's a more accurate measure for determining drug dosages because many physiological processes (like metabolism and heat loss) relate to surface area rather than just body weight.

BSA is used because many physiological functions—cardiac output, metabolic rate, kidney function, and drug metabolism—correlate better with body surface area than weight alone. Chemotherapy drugs, for example, are typically dosed per m² of BSA because this better predicts how the body processes the medication. Using weight alone could result in overdosing obese patients or underdosing smaller patients.

The most common formulas are: DuBois & DuBois (1916): BSA = 0.007184 × Height^0.725 × Weight^0.425—the original and most widely used. Mostov: BSA = √(Height × Weight / 3600)—simplified and equally accurate for most adults. Boyd: More complex but better for children and extreme body types. For clinical use, DuBois is standard, though all formulas give similar results within 5-10% for normal adults.

Average adult BSA ranges from 1.7-2.0 m². Men average about 1.9 m², women about 1.6 m². A 170 cm, 70 kg adult has approximately 1.8 m² BSA. Values below 1.5 m² are considered small, while above 2.2 m² is considered large. Athletes and very tall individuals may have BSA exceeding 2.5 m². Newborns have approximately 0.25 m² BSA.

Chemotherapy doses are calculated as mg/m² of BSA—for example, a drug prescribed at 75 mg/m² for a patient with 1.8 m² BSA equals 135 mg total dose. This method accounts for body size differences better than weight-based dosing. However, BSA-based dosing isn't perfect—it doesn't account for liver/kidney function, genetic differences in drug metabolism, or body composition (muscle vs. fat).