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

What Is Body Surface Area (BSA)?

Body Surface Area (BSA) is a measure of the total surface of the human body, expressed in square metres (m²). Unlike body weight, BSA is a better indicator of metabolic mass because organ size and many physiological functions scale more closely with surface area than with weight.

This BSA Calculator lets you compute your body surface area using five well-known formulas: Du Bois, Mosteller, Haycock, Gehan & George, and Fujimoto. You can work in metric (cm / kg) or imperial (ft / in / lbs) units, choose a specific formula, or compare all five results at once.

We strive to make our calculator as accurate and reliable as possible. However, it is for educational and informational use only and is not a substitute for professional medical advice. For clinical applications such as drug dosing, always consult a qualified healthcare provider.

Why BSA Matters in Medicine

BSA is used across many areas of clinical medicine:

• Chemotherapy dosing — most cytotoxic drugs are dosed in mg/m² to account for differences in body size and to minimise toxicity.
• Cardiac output indexing — cardiac index (CI) = cardiac output ÷ BSA, allowing meaningful comparison across patients of different sizes.
• Burn assessment — estimating the extent of burns expressed as a percentage of total BSA.
• Renal function — GFR is often normalised to 1.73 m² (an average adult BSA) so values are comparable between individuals.
• Paediatric dosing — BSA-based dosing is preferred for children because weight-only dosing can under- or overdose at extreme body compositions.

The Five BSA Formulas

1. Du Bois & Du Bois (1916) — Default

The oldest and most widely cited formula, derived from measurements of nine subjects:

BSA = 0.007184 × W^0.425 × H^0.725

where W is weight in kg and H is height in cm. Despite being over a century old, it remains the reference standard in many pharmacokinetic studies and drug-dosing guidelines.

2. Mosteller (1987)

A simpler approximation that can even be calculated mentally or with a basic calculator:

BSA = √(H × W / 3600)

(height in cm, weight in kg, result in m²). It correlates well with Du Bois for typical adult body sizes and is popular in North American oncology practice.

3. Haycock et al. (1978)

Developed using a broader sample that included infants and children:

BSA = 0.024265 × W^0.5378 × H^0.3964

It tends to give slightly higher estimates than Du Bois in adults and is often preferred for paediatric calculations.

4. Gehan & George (1970)

Derived from a regression analysis of 401 individuals:

BSA = 0.0235 × H^0.42246 × W^0.51456

Produces results close to Du Bois for average adults but diverges at extreme heights or weights.

5. Fujimoto et al. (1968)

Developed specifically from a Japanese population sample:

BSA = 0.008883 × H^0.663 × W^0.444

Tends to yield slightly lower BSA values than Du Bois and may be more accurate for East Asian body proportions.

Typical BSA Values

Reference ranges vary by age and sex, but common benchmarks are:

• Newborn — ≈ 0.25 m²
• 2-year-old child — ≈ 0.5 m²
• 10-year-old child — ≈ 1.1 m²
• Average adult woman — ≈ 1.6 m²
• Average adult man — ≈ 1.9 m²
• Standard normalisation value — 1.73 m²

1.73 m² is the conventional reference surface area used to normalise GFR and certain cardiac measurements — it was based on an early study of healthy adults and has remained the standard ever since.

BSA vs BMI — What Is the Difference?

BMI (Body Mass Index) relates weight to the square of height and is primarily used as a population-level screening tool for underweight, overweight, and obesity. It does not distinguish between muscle and fat, nor does it account for body shape.

BSA estimates the actual surface area of the body and is mostly used for clinical dosing and physiological measurement scaling. A person with the same BMI as another can have a substantially different BSA if they differ in height.

How to Use This Calculator

1. Select your preferred unit system: Metric (cm / kg) or Imperial (ft / in / lbs).
2. Enter your height and weight.
3. Choose a formula — Du Bois is selected by default and is the most widely used.
4. Optionally check "Compare all formulas" to see all five results side by side.
5. Click Calculate.

The result is your estimated BSA in m². You can copy a permanent link to share your result or view it later.

Which Formula Should I Use?

For most healthy adults, all five formulas give very similar results (within ~2–5 % of each other). The choice often depends on context:

• Use Du Bois if your drug protocol or textbook references it specifically — it is the historical standard.
• Use Mosteller if you need a quick mental estimate or your oncology centre uses it.
• Use Haycock for children or infants.
• Use Gehan & George as a cross-check or when a guideline specifies it.
• Use Fujimoto for East Asian populations or when ethnicity-specific accuracy matters.

Frequently Asked Questions

Does BSA change with age?

Yes. BSA increases rapidly during childhood and stabilises in adulthood. Weight gain or loss in adults will change BSA, but the effect is smaller proportionally than the change in weight because BSA scales with weight to a power less than 1 (approximately W^0.44–0.54 depending on the formula).

Why do the formulas give different results?

Each formula was derived from a different study population using different statistical methods. Larger, more diverse samples generally reduce systematic bias, but no single formula is universally "correct." Differences are usually small for typical adult body sizes but become more significant at extremes of height and weight.

Can I use BSA to calculate drug doses myself?

You can calculate the theoretical dose — for example, if a drug is prescribed at 100 mg/m² and your BSA is 1.85 m², the dose would be 185 mg. However, actual dosing must be confirmed by a physician or pharmacist, who will also consider renal function, liver function, body composition, and prior treatment history.

Is BSA accurate for obese or very thin patients?

All formulas become less reliable at extreme body compositions. For obese patients, some clinicians use adjusted or lean body weight rather than actual weight to calculate BSA for chemotherapy dosing, because drug toxicity may otherwise be underestimated. Specialist guidance should be followed.

What units does the calculator output?

The calculator outputs BSA in square metres (m²), which is the universal standard for clinical BSA reporting.