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Free Body Surface Area (BSA) Calculator

This calculator estimates your body surface area (BSA) — the total external area of the body — in square metres (m²) from your height and weight. It uses the Mosteller formula, a simple square-root method that is widely cited for its accuracy and ease of calculation, and it also references the older Du Bois and Du Bois equation as an alternative. BSA is often regarded as a more representative measure of metabolic mass than body weight alone, because it is less affected by abnormal fat mass. The result here is a general-information estimate only and is not medical advice; if BSA matters for a clinical decision, your height and weight should be confirmed and the figure interpreted by a qualified healthcare professional.

Body surface area (Mosteller)
1.82 m²

Mosteller: BSA = √(height·cm × weight·kg ÷ 3600). General information only — not medical advice.

Estimate only. This tool is for general information only and is not medical advice or a diagnosis. Results are estimates based on the formula shown. Consult a qualified healthcare professional for guidance about your own situation.

Quick answer

Body surface area (BSA) is estimated from height and weight. The Mosteller formula gives BSA (m²) = sqrt((height_cm × weight_kg) / 3600). For example, a person 170 cm tall weighing 70 kg has a BSA of about 1.82 m². This is a general estimate, not medical advice.

Formula & method

BSA (m²) = √( height(cm) × weight(kg) / 3600 )

Mosteller formula; the Du Bois formula is an alternative. General information only — not medical advice.

Examples

Example 1: Average adult (Mosteller)
Input
Height 170 cm, weight 70 kg
Result
BSA ≈ 1.82 m²
Why
Multiply 170 × 70 = 11,900, divide by 3600 to get 3.306, then take the square root: sqrt(3.306) ≈ 1.82 m². This is close to the commonly quoted 'average' adult BSA of roughly 1.7–1.9 m².
Example 2: Smaller adult (Mosteller)
Input
Height 160 cm, weight 55 kg
Result
BSA ≈ 1.56 m²
Why
160 × 55 = 8,800; 8,800 / 3600 = 2.444; sqrt(2.444) ≈ 1.56 m². Lower height and weight produce a smaller surface area.
Example 3: Larger adult (Mosteller)
Input
Height 185 cm, weight 95 kg
Result
BSA ≈ 2.21 m²
Why
185 × 95 = 17,575; 17,575 / 3600 = 4.882; sqrt(4.882) ≈ 2.21 m².
Example 4: Mosteller vs Du Bois comparison
Input
Height 170 cm, weight 70 kg
Result
Mosteller ≈ 1.82 m²; Du Bois ≈ 1.81 m²
Why
The Du Bois equation, BSA = 0.007184 × height_cm^0.725 × weight_kg^0.425, gives 0.007184 × 170^0.725 × 70^0.425 ≈ 1.81 m². The two methods usually agree to within a few hundredths of a square metre for typical adults.

When to use this tool

  • When you want a quick general-information estimate of your body surface area in m² from height and weight.
  • When you are curious how your figure compares with the commonly cited 'average' adult BSA of roughly 1.7–1.9 m².
  • When you want to compare the Mosteller and Du Bois methods on the same height and weight.
  • For educational or background reading about how BSA is defined and estimated — not for making medical or dosing decisions, which should be left to a clinician.

Common mistakes

  • Mixing units. The Mosteller formula here expects height in centimetres and weight in kilograms. Entering height in metres or weight in pounds without converting gives a meaningless result.
  • Confusing the divisor. The Mosteller constant is 3600 (so the answer comes out in m²). Some sources write the equivalent inch-and-pound version with a divisor of 3131; do not mix the two.
  • Treating BSA as a body-fat or BMI measure. BSA describes external surface area, not fatness or weight status — it is a different concept from body mass index.
  • Expecting the formula to be exact. All BSA equations are statistical estimates derived from reference populations; they can over- or under-estimate, especially at the extremes of body size or for children with unusual proportions.
  • Using this estimate to calculate medication doses yourself. BSA is sometimes used clinically for dosing, but that calculation must be done and checked by a healthcare professional, not from a general web estimate.

Frequently asked questions

What is body surface area (BSA)?

Body surface area is the total external area of the body, expressed in square metres (m²). Because measuring it directly is impractical, it is normally estimated from height and weight using validated formulas such as Mosteller or Du Bois. It is often considered a better index of metabolic mass than weight alone.

Which formula does this calculator use?

By default it uses the Mosteller formula: BSA (m²) = sqrt((height_cm × weight_kg) / 3600), published by R.D. Mosteller in 1987 as a 'simplified calculation of body-surface area'. The older Du Bois and Du Bois equation, BSA = 0.007184 × height_cm^0.725 × weight_kg^0.425, is a widely used alternative and usually gives a very similar number for typical adults.

What is a normal or average BSA?

For adults the often-quoted average is roughly 1.7 m², with most adults falling somewhere between about 1.5 and 2.2 m² depending on height and build. There is no single 'correct' value — it varies with body size, and these are general reference points rather than health thresholds.

Why is BSA used in medicine?

BSA is used in some clinical contexts because it can correlate better with physiological measures than body weight alone. Any clinical use of BSA, including dose calculations, should be performed and verified by a qualified healthcare professional. This tool provides general information only and is not a substitute for professional medical judgement.

Is this calculator medical advice?

No. It gives a general-information estimate of BSA and is not medical advice, diagnosis, or treatment, and it should not be used to determine medication doses. If a BSA figure matters for your care, please consult a doctor, pharmacist, or other qualified clinician who can confirm your measurements and interpret the result in context.

How accurate is the estimate?

BSA formulas are statistical estimates built from reference populations, so they carry some inherent error and may be less reliable at the extremes of body size, in people with obesity, or in children whose proportions differ from adults. Different formulas can disagree slightly; the value here should be treated as an approximation.

Sources & references

External references open in a new tab. We are independent and not affiliated with these organizations.

Disclaimer

This tool is for general information only and is not medical advice or a diagnosis. Results are estimates based on the formula shown. Consult a qualified healthcare professional for guidance about your own situation.

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  • ✓ Formula and method shown above
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Provided “as is” for general information only — results may be inaccurate, so verify before you rely on them. No warranty; use at your own risk.

Built and reviewed by HIFreeTools against the formula shown above and any authoritative references cited on this page. See our methodology and editorial standards.

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