Calculate body surface area precisely using multiple formulas
Body Surface Area (BSA) expresses the total skin surface of the body in square meters (m²) and is a key indicator in medicine. BSA is essential for determining drug dosage, especially for toxic drugs such as chemotherapy agents. It is also used for cardiac output, kidney function, burn-area calculation, and metabolic rate. Average BSA is about 1.9 m² for adult men and 1.6 m² for women, calculated from weight and height.
The most widely used is the Du Bois formula: BSA (m²) = 0.007184 × weight(kg)^0.425 × height(cm)^0.725, developed in 1916 and standard for over a century. The Mosteller formula is simpler: BSA = √(height(cm) × weight(kg) / 3600). Haycock, Gehan-George, and Boyd formulas are each optimized for specific patient groups. In children, the higher BSA-to-weight ratio means faster drug metabolism, making accurate BSA even more important.
Accurate height and weight must come first. Measure height without shoes while standing upright, and weight on an empty stomach in the morning. For medical use, use the latest clinical measurement and recalculate whenever weight changes. For chemotherapy patients, BSA-based dosing is adjusted each cycle. Muscular or obese individuals may show an overstated BSA, so clinical judgment is needed.
In chemotherapy, BSA is essential — for example, doxorubicin is typically dosed at 60-75 mg/m². In cardiology, the Cardiac Index divides cardiac output by BSA. Nephrology standardizes GFR by BSA. Burn care uses the "rule of nines" to express injury area as a percentage. Anesthesiology considers body surface area when determining anesthetic dosage.
BMI divides weight by height squared to assess obesity, while BSA computes actual surface area to evaluate physiological function. Because BSA combines height and weight, large BMI differences can yield small BSA differences. Obese patients may have relatively little BSA increase despite high body fat, so lipid- and water-soluble drug dosing require different approaches.
Measure weight without clothing weight under consistent conditions, and height with a straight spine. For patients with edema, use dry weight. Standard formulas cannot accurately calculate BSA for amputees, requiring modified formulas or expert judgment. This calculator is for reference only — always consult a physician for actual drug prescriptions.