What is a normal BSA for adults?

In healthy adults, Body Surface Area (BSA) is typically around 1.6–1.9 m² for women and 1.8–2.1 m² for men. However, there is wide variation depending on height, weight, sex, and ethnicity. BSA should always be interpreted in clinical context rather than as a strict normal/abnormal cutoff.

Which BSA formula should I use?

Mosteller is the most widely used BSA formula in clinical practice because it is simple and agrees reasonably well with more complex formulas. Du Bois is the historical reference standard. Haycock, Boyd, and Gehan–George may be preferred in pediatrics or for very small or very large body sizes. In most adult dosing situations, using the same formula consistently is more important than which specific formula you choose.

Is BSA better than BMI?

BSA and BMI measure different things. BMI is weight relative to height and is used to classify underweight, normal weight, overweight, and obesity. BSA estimates the total external surface area of the body and is used to scale physiological processes and medication doses (for example, chemotherapy, some antibiotics, and cardiac index). Neither replaces a full clinical assessment.

Can I use this BSA calculator for children?

Yes. This calculator supports pediatric BSA estimation and includes formulas such as Haycock, Boyd, and Gehan–George that were validated in children. Always double-check pediatric drug doses and follow local pediatric dosing guidelines.

How accurate are BSA formulas?

All BSA formulas are approximations based on population studies. For most clinical uses, differences between formulas are within 5–10%. Accuracy may be lower in extremes of body size, severe obesity, edema, or cachexia. When dosing high-risk medications, clinicians may adjust doses based on response, organ function, and therapeutic drug monitoring rather than BSA alone.

BSA Calculator – Body Surface Area (Mosteller, Du Bois, Haycock)

What is Body Surface Area (BSA)?

Body Surface Area (BSA) is an estimate of the total external surface area of the human body, expressed in square meters (m²). It is widely used in medicine to:

Calculate drug doses (for example, chemotherapy, some antibiotics, heparin)
Normalize physiological measurements (for example, cardiac index, glomerular filtration rate)
Estimate metabolic needs and fluid requirements

Directly measuring body surface area is impractical, so clinicians use empirical formulas based on height and weight.

Most common BSA formulas

This calculator computes BSA using several widely cited formulas.

1. Mosteller formula (simple and widely used)

Mosteller (1987):

\( \text{BSA}_{Mosteller} = \sqrt{\dfrac{\text{height (cm)} \times \text{weight (kg)}}{3600}} \)

The Mosteller formula is popular because it is easy to remember and gives results close to more complex formulas for most adults and children.

2. Du Bois & Du Bois formula (historical reference)

Du Bois (1916):

\( \text{BSA}_{DuBois} = 0.007184 \times \text{height (cm)}^{0.725} \times \text{weight (kg)}^{0.425} \)

Du Bois & Du Bois is one of the earliest BSA formulas and is still used as a reference in many pharmacology studies.

3. Haycock formula (often used in pediatrics)

Haycock (1978):

\( \text{BSA}_{Haycock} = 0.024265 \times \text{height (cm)}^{0.3964} \times \text{weight (kg)}^{0.5378} \)

The Haycock formula was derived from a pediatric population and performs well in infants and children as well as adults.

4. Boyd formula (adjusts for body weight)

Boyd (1935):

First compute \( W = \text{weight (kg)} \). Then:

\( \text{BSA}_{Boyd} = 0.0003207 \times \text{height (cm)}^{0.3} \times \left( 1000 \times W \right)^{0.7285 - 0.0188 \log_{10}(1000W)} \)

Boyd’s formula attempts to better handle extremes of body size, especially in children and very small adults.

5. Gehan & George formula

Gehan–George (1970):

\( \text{BSA}_{Gehan} = 0.0235 \times \text{height (cm)}^{0.42246} \times \text{weight (kg)}^{0.51456} \)

Gehan–George is another alternative that has been validated in both adults and children, with results similar to Du Bois and Haycock.

Example calculation

Consider an adult with:

Height = 170 cm
Weight = 70 kg

Using the Mosteller formula:

\( \text{BSA} = \sqrt{\dfrac{170 \times 70}{3600}} = \sqrt{\dfrac{11900}{3600}} \approx \sqrt{3.3056} \approx 1.82 \,\text{m}^2 \)

Typical BSA ranges

Approximate BSA ranges (Mosteller or Du Bois):

Newborn: ~0.20–0.25 m²
1-year-old: ~0.40–0.45 m²
10-year-old: ~1.0–1.3 m²
Adult woman: ~1.6–1.9 m²
Adult man: ~1.8–2.1 m²

These are rough reference values. Individual patients may fall outside these ranges and still be healthy.

Clinical uses of BSA

Drug dosing: Many chemotherapy regimens are prescribed in mg/m² of BSA.
Cardiology: Cardiac index (CI) = cardiac output / BSA.
Nephrology: GFR is often normalized to 1.73 m² of BSA.
Critical care: Fluid resuscitation and nutritional needs may be scaled to BSA.

Always follow local protocols and drug monographs; BSA is only one factor in safe dosing.

Limitations and caveats

BSA formulas are based on population averages and may be less accurate in extremes of body size, obesity, edema, or cachexia.
Different formulas can differ by 5–10% or more for the same patient.
For high-risk drugs (for example, chemotherapy), clinicians may adjust doses based on toxicity, organ function, and therapeutic drug monitoring.

Important: This tool is for educational and clinical support purposes only and does not replace professional medical judgement.

Body Surface Area (BSA) Calculator

BSA Calculator

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How to interpret BSA