Body Surface Area (BSA) Calculator

Body Surface Area (BSA) is the measured or estimated total surface area of the human body, expressed in square meters (m²). It is clinically important because BSA correlates better than weight alone with key physiological parameters such as cardiac output, renal clearance, and metabolic rate. BSA is the standard basis for chemotherapy dosing in oncology (most cytotoxic agents are dosed in mg/m²), cardiac index calculation (CI = CO/BSA), and pediatric drug dosing. The average adult BSA is approximately 1.7–1.9 m² for women and 1.9–2.1 m² for men.

The Du Bois formula (Du Bois D & Du Bois EF, Arch Intern Med 1916) is: BSA = 0.007184 × H^0.725 × W^0.425, where H is height in cm and W is weight in kg. Despite being derived from only 9 subjects, it remained the gold standard for over a century because it gave consistent results in adults of average size and its values were used to calibrate cardiac output equipment. Most oncology dosing tables and cardiac catheterization labs still use Du Bois as their reference.

The Mosteller formula (NEJM 1987) simplifies BSA calculation to: BSA = √(H × W / 3600). It is popular in oncology and critical care because of its arithmetic simplicity — it can be estimated mentally or with a basic calculator. Studies comparing all formulas show Mosteller gives results within 1–2% of Du Bois for most adult patients. It is the preferred formula in many North American oncology protocols and pharmacy software systems.

The Haycock formula (Haycock GB et al., J Pediatr 1978) is considered most accurate for children and infants: BSA = 0.024265 × H^0.3964 × W^0.5378. It was specifically validated across a pediatric population ranging from premature infants to adolescents. The Gehan-George formula is also widely used in pediatric oncology. For clinical pediatric dosing, always verify which formula your institutional protocol specifies, as using the wrong formula can result in significant dosing errors.

Most cytotoxic chemotherapy agents (including platinum compounds, taxanes, anthracyclines, and fluorouracil) are dosed in mg/m² of BSA. This approach distributes drug exposure more uniformly across body sizes than weight-based dosing, since drug clearance by the kidneys and liver correlates more closely with BSA. A standard dose for a 1.73 m² patient (the historical reference BSA) is scaled up or down proportionally. Some protocols also cap doses at a maximum BSA (typically 2.0 m²) to prevent toxicity in very large patients. Never use BSA calculators as the sole basis for clinical dosing without physician verification.

Cardiac Index (CI) = Cardiac Output (CO) / BSA. It normalizes cardiac output to body size, making it comparable across patients. Normal CI is 2.5–4.0 L/min/m². A CI below 2.2 L/min/m² suggests cardiogenic shock; above 4.0 may indicate high-output states (sepsis, hyperthyroidism, arteriovenous fistula). BSA is also used to calculate GFR correction (eGFR normalized to 1.73 m²), renal function assessment, and oxygen consumption index in hemodynamic monitoring.