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Body surface area (BSA)

Body Surface Area Calculator: 8 Medical Formulas

Calculate BSA using 8 clinical formulas including Mosteller, Du Bois, and Haycock. Essential for chemotherapy dosing, cardiac index, and metabolic assessment. Compare formula results with consensus averaging.

By Jeff Beem

Updated

Estimates only, not a substitute for clinical dosing decisions.

01

Inputs

Used for the Schlich equation only.

ft
in
02

Formula

Average of all formulas for maximum reliability

03

Results

Body surface area about 1.934 square meters. Size band: Average adult. Model: Consensus (Mean).

Metabolic mass
149.2
lbs (est.)
Formula variance
3.7%
Max vs mean
All models
Mosteller(1987)
1.952m²
Du Bois & Du Bois(1916)
1.948m²
Haycock(1978)
1.958m²
Gehan & George(1970)
1.962m²
Boyd(1935)
1.961m²
Fujimoto & Takahira(1968)
1.897m²
Schlich(2010)
1.862m²
Consensus mean
1.934m²

Why BSA matters

Body surface area tracks metabolic rate, drug distribution, and cardiac index better than BMI alone because it scales with heat exchange area, not only mass.

Drug dosing

Many chemotherapies and critical meds use mg per m² BSA for therapeutic targeting.

Cardiac index

Cardiac output divided by BSA normalizes pump function across body sizes.

Metabolic rate

BSA aligns with resting energy needs more closely than weight alone.

Reference BSA by cohort

Illustrative averages across the lifespan.

Newborn
BSA
0.25 m²
Weight
3.5 kg
Height
50 cm
Infant (1 yr)
BSA
0.45 m²
Weight
10 kg
Height
75 cm
Child (5 yr)
BSA
0.75 m²
Weight
18 kg
Height
110 cm
Child (10 yr)
BSA
1.14 m²
Weight
32 kg
Height
140 cm
Adolescent (15 yr)
BSA
1.60 m²
Weight
55 kg
Height
165 cm
Adult Female (avg)
BSA
1.70 m²
Weight
62 kg
Height
163 cm
Adult Male (avg)
BSA
1.90 m²
Weight
75 kg
Height
175 cm
Large Adult
BSA
2.20 m²
Weight
95 kg
Height
185 cm

170 cm, 70 kg → about 1.82 m²

That is the Mosteller shortcut for a typical adult build. Hospitals use body surface area (BSA) to scale some drug doses and physiologic indices because metabolic demand and distribution volume track size more closely than weight alone in many settings. This calculator runs seven published formulas plus a simple mean (consensus) so you can compare them side by side.

Four things worth knowing

Seven formulas, one consensus line

Mosteller, Du Bois, Haycock, Gehan & George, Boyd, Fujimoto & Takahira (one combined formula here), and Schlich (sex-specific). Consensus is the arithmetic mean of those seven. Formulas usually agree within a few percent on average adults; wider spread is a signal to use clinical judgment, not panic.

The 2.0 m² cap is a protocol choice

Some chemotherapy regimens cap the BSA used for dosing at 2.0 m² even when the measured estimate is higher. The idea is that drug handling does not scale forever with size. Your protocol may or may not use a cap; the raw calculator number is not automatically the dose BSA.

Kids are not small adults geometrically

Children have more surface area per unit of body weight than adults. That is why pediatric dosing often specifies Haycock or another pediatric-derived formula instead of Du Bois alone. Under 18, start with Haycock unless your reference says otherwise.

Same height and weight, different bodies

BSA formulas only see height and weight. Two people with identical numbers get identical BSA, whether one is muscular and one is not. For obesity or very low BMI, the tool may show a warning and formula disagreement above about 10%; treat that as a reason to double-check, not as a diagnosis.

Body surface area calculator: seven formulas and consensus

170 cm and 70 kg → about 1.82 m² (Mosteller). Compare Du Bois, Haycock, Boyd, and others, or use the mean of all seven. For education only; not medical advice.

What this calculator does

Estimates body surface area in square meters from height and weight using seven clinical formulas, plus a consensus value (their average). You can switch units, pick a formula, and see all results at once with how far they spread.
  • Outputs:
    Primary BSA (m²) for the selected formula, all seven formula values, consensus mean, a simple size band (infant through large adult), and a variance note when spread exceeds about 10%.
  • Limits:
    Not for prescribing. Does not apply protocol caps (e.g. 2.0 m² chemo caps), ideal body weight, or adjusted body weight rules. Schlich needs sex; Fujimoto & Takahira are one combined formula in code, not two separate lines. Calculations run in your browser; nothing is uploaded.

The math

All formulas take height (cm) and weight (kg) internally. Imperial entries convert first.
  • Mosteller (1987):
    BSA=H×W3600\text{BSA} = \sqrt{\frac{H \times W}{3600}}

    Example: 170 cm, 70 kg → about 1.82 m².

  • Du Bois (1916):
    BSA=0.007184×W0.425×H0.725\text{BSA} = 0.007184 \times W^{0.425} \times H^{0.725}

    Still common in older protocols.

  • Haycock (1978):
    BSA=0.024265×W0.5378×H0.3964\text{BSA} = 0.024265 \times W^{0.5378} \times H^{0.3964}

    Often used for pediatrics.

  • Also included:
    Gehan & George, Boyd, Fujimoto & Takahira (single combined formula), and Schlich (male vs female). Consensus = mean of those seven values.
  • Where BSA shows up:
    Chemotherapy mg/m² dosing, cardiac index (output ÷ BSA), GFR normalized to 1.73 m², and burn “rule of nines” percentages. Each setting has its own rules; this page only computes m².

Using the calculator

Pick metric or imperial, enter height and weight, choose a formula or Consensus, and read m². Expand the comparison table to see every formula at once.
  • Formula picks:
    Adults: Mosteller or Du Bois for a single number. Under 18: Haycock. East Asian cohorts: some references mention Fujimoto; use what your protocol specifies. Consensus when you want the average and the spread.
  • Variance note:
    The UI flags when the max deviation from the mean is above about 10% (not 5%). Large spread or BMI warnings mean the estimate is less stable.
  • Reference bands:
    Built-in examples (newborn ~0.25 m², average woman ~1.7 m², average man ~1.9 m²) help sanity-check your inputs.
  • Privacy:
    Runs locally in the browser.

FAQ

Which BSA formula should I use?

For a quick adult estimate, Mosteller is enough. Many drug protocols still reference Du Bois. For patients under 18, pick Haycock. Consensus averages all seven formulas in this tool (not a published standard, but useful when you want one number and a spread). Always follow the protocol your clinician or reference gives you.

How is BSA used in medicine?

Oncology often doses cytotoxic drugs per m². Cardiac index divides cardiac output by BSA. GFR is sometimes reported normalized to 1.73 m². Burn charts and some ventilator targets also refer to body size. BSA is a scaling shortcut, not a perfect stand-in for metabolism in every patient.

What is a typical adult BSA?

Rough population averages: about 1.7 m² for women and 1.9 m² for men. Healthy adults often fall in the 1.5–2.2 m² range. Newborns are near 0.25 m² and approach adult values in late adolescence.

How is BSA different from BMI?

BMI is weight divided by height squared. BSA estimates total skin surface from height and weight with a nonlinear formula. BMI screens weight status; BSA scales some clinical doses and indices. They answer different questions.

Can I get BSA from a bathroom scale alone?

No. You need height and weight (and for Schlich, sex). Some smart scales estimate BSA from a profile, but clinical work should use measured height/weight and the formula your protocol names.

Why do some chemo protocols cap BSA at 2.0 m²?

Very large calculated BSA can push mg/m² doses higher than clinicians want. Some protocols cap at 2.0 m² because clearance does not keep rising linearly with size. That cap is protocol-specific; do not assume every regimen uses it.

How do I check Mosteller by hand?

BSA = √((height cm × weight kg) / 3600). Example: 170 cm and 70 kg → √(11,900 / 3600) = √3.306 → about 1.82 m².

Is BSA the same as body fat percentage?

No. BSA is surface area in m². Body fat percentage is fat mass relative to weight. This page estimates BSA only.

Sources & citations

References used for the calculation method and definitions. Links open in a new tab when available.

[1]
Du Bois D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med. 1916;17:863-871

Original Du Bois BSA formula, still the clinical standard for drug dosing and cardiac index normalization.

[2]
Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987;317(17):1098

Mosteller simplified BSA formula widely used for bedside estimation and chemotherapy dosing.

[3]
Haycock GB, Schwartz GJ, Wisotsky DH. Geometric method for measuring body surface area. J Pediatr. 1978;93(1):62-66

Haycock BSA formula optimized for pediatric and neonatal patients with different body proportions.

Fitness Reference Note

Informational Use: These calculations (BMI, Calories, etc.) are based on standard statistical formulas and are intended for general reference and goal-setting purposes only.

Consult Experts: This tool does not provide medical advice, diagnosis, or treatment. Results may not be accurate for athletes, pregnant individuals, or those with underlying health conditions.

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