Body Surface Area Calculator

Body Surface Area Calculator — evidence-based tool to check your body surface area. Includes formula, tips, and interpretation guide.

The Body Surface Area Calculator is a focused tool for an estimate of the body's external surface area from height and weight. Body surface area (BSA) is a calculated estimate expressed in square metres. It is used as a scaling variable in some clinical, pharmacological, physiological, and research contexts because height and weight together can describe body size differently from body mass alone. This page is deliberately separate from body-fat estimation: BSA does not estimate fat percentage, lean mass, or health risk. For broader context, compare the result with the BMI calculator and the body-fat calculator rather than treating one body-composition measure as a complete health assessment.

Use the height and weight that belong to the same time point. Height should be standing height without shoes, and weight should be measured with a consistent level of clothing and equipment. For a clinical decision, use the measurements recorded by the care team. The calculator is intentionally transparent: it shows the input units, the equation, and the assumptions that shape the output. It does not use hidden population averages to turn a simple measurement into a diagnosis, treatment recommendation, or guaranteed prediction.

Use the page for an identified question and a repeatable comparison. Decide the measurement protocol before collecting data, write down the date and units, and avoid changing several inputs or methods at once. That makes a trend easier to interpret and makes it clear when a result is only a change in measurement conditions.

Choose a unit system and use it consistently for every input on the page.
Collect the measurements under the conditions described in the calculator and in your local guidance.
Enter the values without swapping the starting and current time points or mixing units.
Read the result together with the formula and the assumptions; do not infer more precision than the inputs justify.
Repeat the measurement with the same method if the value is unexpected or materially different from the previous result.
Record the raw inputs, date, method, and any relevant context so the next comparison is meaningful.

Body Surface Area: formula and assumptions

Du Bois BSA = 0.007184 × height(cm)^0.725 × weight(kg)^0.425. The exponents make this a nonlinear size estimate, so doubling one input does not simply double the final area.

At 175 cm and 70 kg, the Du Bois estimate is about 1.84 m². Rounding the inputs before calculation can move the final value slightly, so the displayed result should be treated as an estimate rather than a directly measured surface.

The formula is a calculation model, not a direct measurement of tissue, risk, fitness, or treatment need. It is only valid when its inputs are positive and expressed in the units expected by the equation. The page rejects impossible or directionally inconsistent inputs rather than manufacturing a finite-looking answer.

For background, see The original Du Bois and Du Bois body-surface-area study. Source definitions, measurement sites, and reference populations should be checked whenever this value is used in a formal health, sport, or research setting.

How to read the result

A reference point, not a verdict

BSA is a useful common denominator in selected protocols, but it is not a universal dosing rule. Some medicines use fixed doses, body weight, ideal body weight, adjusted body weight, renal function, or an independently specified protocol. A clinician or pharmacist must choose the dosing method; this calculator cannot do that safely.

Read the displayed number at the precision supported by the measurement. A calculator may show several decimal places because the equation is numeric, but that does not mean a tape measure, home scale, or body-fat device can support that precision. Compare like with like and focus on a consistent direction over a suitable interval.

If the result conflicts with symptoms, a clinician's assessment, or a formal protocol, the qualified professional and the current protocol take priority. Use this page to prepare questions and organise measurements, not to delay care or make a treatment decision independently.

Health tips and best practices

Keep centimetres and kilograms as the input units; convert imperial measurements before entering them.
Use the same formula when comparing two results, because Mosteller, Haycock, Gehan–George, and Du Bois will not give identical numbers.
Record the formula name next to the result when BSA is being passed to a clinician or included in a worksheet.
Do not use a BSA result to change a medicine dose, infusion rate, chemotherapy protocol, or burn-treatment plan.
Small changes in weight may have little practical meaning when the measurement uncertainty is larger than the difference.
When a protocol specifies a different BSA equation, its named equation takes priority over this page.

The result is shown in m², even though the inputs are a height and a mass.
The Du Bois equation was derived from a small historical sample and remains a conventional estimate, not a direct skin measurement.
Two accepted BSA equations can differ by a few percentage points for the same person.
A formula output is not evidence that a drug or treatment should be scaled to BSA.

Common mistakes to avoid

Entering height in metres when the formula expects centimetres, producing a severe unit error.
Using pounds as though they were kilograms.
Comparing a Du Bois result with a result from another equation without naming the equation.
Assuming BSA is body surface area measured by imaging or a substitute for body-composition testing.
Applying the number directly to treatment without checking the current prescribing information and clinical protocol.

This calculator is for general educational and tracking purposes only. It does not diagnose disease, prescribe treatment, determine medication dose, replace a clinician's assessment, or guarantee a fitness or weight-management outcome. Measurement error and individual context can materially affect interpretation. If you are concerned about a health change, are pregnant or postpartum, are under 18, have a chronic condition, take medication, or have a history of disordered eating, discuss the question with an appropriately qualified healthcare professional.