Body Surface Area (BSA) Calculator

What is Body Surface Area (BSA)?

Body Surface Area (BSA) is the measured or calculated surface of a human body. For many clinical purposes, BSA is a better indicator of metabolic mass than body weight because it is less affected by abnormal adipose mass (fat). In medicine, physiology, and pharmacology, BSA is the "gold standard" for normalizing physiological parameters like cardiac output and for calculating dosages for certain medications.

Why is BSA Important in Medicine?

Unlike BMI, which is a screening tool for weight categories, BSA is a precise metric used for:

• Chemotherapy Dosing: Many anti-cancer drugs are dosed in mg/m² to minimize toxicity and maximize efficacy.
• Cardiac Index: To assess heart performance, doctors divide Cardiac Output by BSA. This allows them to compare heart function between a small person and a large person.
• Glomerular Filtration Rate (GFR): Kidney function is often normalized to a standard BSA of 1.73 m². (See our GFR Calculator).
• Burn Treatment: Determining fluid replacement needs often depends on the percentage of BSA affected (Parkland formula).

The Formulas: Which One Should You Use?

Direct measurement of BSA is difficult, so mathematical formulas are used. While they all yield similar results, some are preferred in specific contexts.

1. Mosteller Formula (1987)

$$ \text{BSA} = \sqrt{\frac{\text{Height (cm)} \times \text{Weight (kg)}}{3600}} $$
This is the most common formula used today because it is mathematically simple and easy to remember. It is widely adopted in electronic medical records and pharmacy trials.

2. Du Bois & Du Bois (1916)

For decades, this was the standard. While accurate, the calculation is more complex. It remains a benchmark for comparing other formulas.

3. Haycock (1978)

Often preferred in pediatrics (children) because it was validated across a wider range of body sizes, from infants to adults.

4. Gehan & George (1970)

Another variation used in some specific cancer treatment protocols.

5. Boyd (1935)

Considered by some statisticians to be mathematically superior at the extremes of body size (very small or very large individuals).

Average BSA Values

While everyone is different, here are general reference ranges:

• Neonates: 0.25 m²
• Children (2 years): 0.5 m²
• Children (10 years): 1.14 m²
• Adult Women: 1.6 m²
• Adult Men: 1.9 m²