Body Surface Area Calculator

A Vital Metric in Medicine: The Body Surface Area (BSA) Calculator

Body Surface Area (BSA) is a measurement of the total surface area of the human body. While it might seem like an obscure metric, it is of critical importance in many fields of medicine, particularly in oncology and pharmacology. For many drugs, especially chemotherapeutic agents, the correct dosage is determined by the patient's BSA rather than their body weight alone. The theory is that BSA provides a more accurate measure of a patient's metabolic mass and physiological function than simple weight, which can be skewed by factors like obesity or edema. By dosing based on surface area, clinicians can provide a more individualized and effective treatment, minimizing toxicity and maximizing therapeutic benefit.

Over the years, several formulas have been developed to estimate BSA from a patient's height and weight, as direct measurement is impractical. This calculator uses one of the most widely used and validated of these formulas: the Du Bois & Du Bois formula. By simply entering a patient's height and weight, this tool provides a quick and accurate estimation of their BSA, which is an essential first step for any healthcare professional prescribing a BSA-based medication. It eliminates the need for manual calculations, reducing the risk of error in a clinical setting where precision is paramount.

The Du Bois Formula Explained

The Du Bois formula, published in 1916, is a classic and still widely used method for estimating Body Surface Area. It was derived from direct measurements of a small number of subjects and has stood the test of time as a reliable estimator.

The Formula: BSA (m²) = 0.007184 × Weight (kg)⁰.⁴²⁵ × Height (cm)⁰.⁷²⁵

Where:

• BSA is the Body Surface Area, expressed in square meters (m²).
• Weight is the patient's weight in kilograms (kg).
• Height is the patient's height in centimeters (cm).

This calculator handles the necessary unit conversions and the complex exponential calculations to provide an immediate result.

Clinical Applications of BSA

The primary use of BSA is to calculate the dosage of drugs that have a narrow therapeutic index, meaning the range between a therapeutic dose and a toxic dose is small. Dosing based on BSA helps to normalize the drug exposure across patients of different sizes.

• Chemotherapy: This is the most common application. Most chemotherapy drugs are dosed based on mg/m², so calculating the patient's BSA is the first step in determining their specific dose.
• Cardiology: The cardiac index is a measure of cardiac output divided by the BSA, providing a measure of heart performance relative to body size.
• Glomerular Filtration Rate (GFR): In nephrology, GFR is often normalized to a standard BSA of 1.73 m² to allow for comparison of kidney function between individuals of different sizes.