Body Surface Area

Body surface area, often abbreviated as BSA, is a measurement that quantifies the total external surface area of the human body. It is a crucial biometric parameter in medicine and physiology, as it correlates better with certain metabolic functions, such as basal metabolic rate and cardiac output, than body weight alone. Its most critical application is in drug dosing, particularly for chemotherapeutic agents and other drugs with a narrow therapeutic index, where the dose is often calculated in milligrams per square meter (mg/m²) to minimize toxicity and optimize efficacy. Beyond oncology, BSA is used in intensive care, in physiological studies to calculate the cardiac index (cardiac output per BSA), and in assessing the severity of burns (although the "Rule of Nines" is used to estimate the *percentage* burned, the total BSA is the denominator). As direct measurement of BSA is impractical, it is estimated using mathematical formulas, called allometric equations. These formulas, such as the Mosteller formula (the most common currently), the Du Bois and Du Bois, or the Haycock formula, use the patient's weight (mass) and height (stature) to calculate the value, which is expressed in square meters (m²). For an average adult, the BSA is typically around 1.7 to 1.9 m².