Free Body Surface Area (BSA) Calculator

The Body Surface Area (BSA) calculator is a practical medical tool that estimates the external surface area of a person’s body, expressed in square meters. BSA is often considered more informative than body weight alone when assessing metabolic rate, and it plays a key role in determining medication dosages, particularly for treatments with narrow safety margins such as chemotherapy. Clinicians and physiologists rely on body surface area formulas to derive this metric from basic anthropometric measurements.

BSA Formulas in Common Use

The BSA medical literature describes several validated equations. The Du Bois formula remains one of the most widely used, and many BSA calculators adopt it as the default. Other established formulas include Mosteller, Haycock, Gehan & George, and Fujimoto — all of which require only weight and height. Below are the standard expressions (weight in kilograms, height in centimeters, BSA in square meters):

• Du Bois formula:
  $\text{BSA} = 0.007184 \times \text{weight}^{0.425} \times \text{height}^{0.725}$

• Mosteller formula:
  $\text{BSA} = \sqrt{ \dfrac{\text{weight} \times \text{height}}{3600} }$

• Haycock formula:
  $\text{BSA} = 0.024265 \times \text{weight}^{0.5378} \times \text{height}^{0.3964}$

• Gehan & George formula:
  $\text{BSA} = 0.0235 \times \text{weight}^{0.51456} \times \text{height}^{0.42246}$

• Fujimoto formula:
  $\text{BSA} = 0.008883 \times \text{weight}^{0.444} \times \text{height}^{0.663}$

For a quick manual approximation, the Mosteller formula is straightforward. Suppose a person is 170 cm tall and weighs 60 kg: multiply height by weight (170 × 60 = 10,200), divide by 3600 (≈ 2.833), and take the square root (≈ 1.68 m²). This near‑1.7 m² result aligns with the averages seen in adults.

How the BSA Calculator Works

Using this body surface area calculator eliminates tedious hand calculations. You simply enter your height and weight (the tool accepts both metric and imperial units), and it instantly computes your BSA based on your chosen formula. For the same example of 170 cm and 60 kg, the calculator returns approximately 1.69 m² — a slight variation due to the specific equation used. The instrument is designed for speed and accuracy, making it ideal for bedside or office use.

Typical BSA Values by Age and Sex

Knowing average BSA figures helps contextualize your result. The following table summarizes reference values:

Category	Average BSA (m²)
Infants	0.25
Children (2 years)	0.50
Children (10 years)	1.14
Women (adult)	1.60
Men (adult)	1.90

The widely cited reference BSA of 1.73 m² corresponds to a roughly 70 kg adult and is often used in estimating glomerular filtration rate (GFR).

Clinical Considerations and Limitations

While BSA is a valuable metric, it is not without criticism. The most important caution involves using BSA for dose calculations of high‑risk drugs, especially cytotoxic agents, where small errors can have serious consequences. BSA‑based dosing has come under scrutiny for its variability across body compositions and ethnic groups. Always consult a healthcare provider before applying any BSA‑derived dosage. For a fuller picture of health, complementary tools such as BMI calculators and water intake trackers can be useful, but they are not substitutes for professional medical judgment.