BYTETOOLS

Body Surface Area Calculator

Calculate body surface area in m² with the Du Bois, Mosteller, Haycock, Boyd and Gehan-George formulas side by side, in metric or imperial units.

Body surface area

2.00 m²

Mean of the five formulas below for 180.0 cm and 80.0 kg. They disagree by 0.013 m² (0.7%) at this body size — that spread is the honest uncertainty in any BSA figure.

2.00 m²
Mosteller BSA
2.00 m²
Du Bois BSA
0.013 m²
Spread between methods
24.7
BMI (for context)

Formula by formula

FormulaBSA (m²)vs meanCalculation
Du Bois & Du Bois
The 1916 original; still the reference in much of the cardiology and physiology literature.
1.996−0.0080.007184 × 180.0^0.725 × 80.0^0.425
Mosteller
The 1987 simplification most oncology services use for chemotherapy dosing — easy to check by hand.
2.000−0.004√(180.0 × 80.0 / 3600)
Haycock
Derived from a sample that included infants and children, so it behaves better at small body sizes.
2.007+0.0030.024265 × 180.0^0.3964 × 80.0^0.5378
Boyd
Uses a weight-dependent exponent, which keeps it closer to measured values across a wide weight range.
2.007+0.0030.0003207 × 180.0^0.3 × (grams)^(0.7285 − 0.0188 × log₁₀ grams)
Gehan & George
Fitted to 401 direct surface-area measurements; often the closest to Du Bois for average adults.
2.009+0.0060.0235 × 180.0^0.42246 × 80.0^0.51456

Every formula takes height in centimetres and weight in kilograms (Boyd converts weight to grams internally), so imperial inputs are converted first. Sanity check: 180 cm and 80 kg gives exactly 2.00 m² under Mosteller, which is the standard worked example for this equation.

Estimates only. This tool does not diagnose anything and it is not medical advice, and it must never be used to work out a drug dose. BSA formulas are regressions fitted to small samples — Du Bois used nine subjects — and they are least reliable in infants, in very obese people and at the extremes of height. Clinical BSA dosing follows local protocol, uses a specific formula chosen by the service, and is checked by a pharmacist. If a number here matters to you, take it to your clinician.

What is the Body Surface Area Calculator?

Body surface area is the total external area of the body in square metres, estimated from height and weight. The Mosteller formula, BSA = √(height in cm × weight in kg ÷ 3600), is the simplest and most widely used.

  • Five BSA formulas calculated side by side with their exact expressions
  • Shows the spread between methods in m² and as a percentage
  • Metric and imperial input with automatic conversion
  • BMI shown alongside for context
  • Plain-English note on the origin of each formula
  • 100% client-side — height and weight never leave your browser

How to use the Body Surface Area Calculator

  1. 1

    Choose metric (cm, kg) or imperial (ft/in, lb) units.

  2. 2

    Enter your height and your weight.

  3. 3

    Read the averaged body surface area at the top.

  4. 4

    Compare the five formulas and the spread between them in the table.

  5. 5

    Note which formula your clinician or protocol actually uses before quoting a number.

About the Body Surface Area Calculator

The ByteTools Body Surface Area Calculator estimates BSA in square metres from your height and weight, running five published formulas at once: Du Bois and Du Bois, Mosteller, Haycock, Boyd and Gehan-George. Showing them together makes the disagreement between methods visible, which matters because different services use different formulas and the choice can shift the answer by a few percent.

Each row shows the formula, the resulting BSA, and how far it sits from the mean of the five, along with a note on where that particular equation came from and what it is good at. A useful sanity check: 180 cm and 80 kg gives exactly 2.00 m² under Mosteller, which is the standard worked example for that equation.

Enter your measurements in metric or imperial — feet and inches are converted internally — and everything is computed in your browser with nothing uploaded. Estimates only, not medical advice and not a diagnosis. BSA must never be used here to work out a drug dose; clinical dosing follows local protocol, uses a specific chosen formula, and is checked by a pharmacist.

Frequently asked questions

What is the average body surface area for an adult?

Roughly 1.7 m² is the figure most often quoted for an average adult, with about 1.9 m² typical for men and 1.6 m² for women. A person of 180 cm and 80 kg comes out at close to 2.0 m² on every formula on this page.

Which BSA formula should I use?

Mosteller is the most common in practice because it is simple enough to verify by hand and agrees closely with the older Du Bois equation for typical adults. Haycock behaves better in children, and Boyd holds up better across a wide weight range. If a clinical decision depends on it, use whichever formula your local protocol specifies.

How accurate are body surface area formulas?

Less accurate than their three-decimal output suggests. They are regressions fitted to small samples — the original Du Bois equation used just nine subjects — and validation studies find errors of several percent against direct measurement, with the largest errors in infants, in very obese people and at extremes of height. That is why this tool shows five formulas and the spread between them rather than one number.

Why is body surface area used instead of weight?

Because several physiological quantities — cardiac output, glomerular filtration rate, metabolic rate — scale more closely with surface area than with body mass. Indexing to BSA lets clinicians compare people of very different sizes on a common footing.

Can I use this to calculate a chemotherapy dose?

No. Never use a web calculator for drug dosing. Clinical BSA dosing uses a formula specified by the treating service, applies capping rules for very large or very small patients, and is independently checked by a pharmacist. If you want to understand your own dose, ask your oncology team.

How do I convert my height and weight?

You do not have to — switch the units toggle to imperial and enter feet, inches and pounds, and the tool converts to centimetres and kilograms internally before applying any formula. Every published BSA equation expects metric input.

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