Body Surface Area Calculator - BSA Calculator & Medical Dosing Calculator

BSA is often used in clinical purposes over body weight because it is a more accurate indicator of metabolic mass (the body's need for energy). Metabolic mass can be estimated using fat-free mass, where fat-free mass is all of a person's body mass that does not include fat. This includes bones, tendons, inner organs, muscles, blood, nerves, and more. Since body fat is not metabolically active and fat-free mass excludes body fat, fat-free mass is a reasonable estimate of metabolic mass.

BSA is also used in various other clinical settings, such as determining cardiac index (to relate a person's heart performance to their body size) or most commonly, dosages for chemotherapy (a category of cancer treatment). While dosing for chemotherapy is often determined using a patient's BSA, there exist arguments against the use of BSA to determine medication dosages that have a narrow therapeutic index – the comparison of the amount of a substance necessary to produce a therapeutic effect, to the amount that causes toxicity. If the therapeutic index is too narrow, BSA may not be an accurate enough measure, and there is a risk of causing a toxic rather than therapeutic effect. There is also evidence that BSA becomes less accurate at the extremes of height and weight, and BMI may be a better estimate in such cases. Despite these limitations, the effects of chemotherapy dosages as determined by BSA measurements still remain more consistent than those determined by body weight alone.