The Body Surface Area Calculator estimates the external surface of the body in square metres from height and weight. Enter centimetres and kilograms (or US units for conversion), choose a formula if needed, and the tool returns BSA with Mosteller as the default alongside Du Bois, Haycock and Gehan-George for comparison.
BSA appears in clinical work such as chemotherapy dosing and cardiac index calculations. This page computes the educational figure and stops there. Interpretation of a result, and any decision about medicine doses, belong with a qualified clinician who has the full chart in hand. A web estimate is not a prescription aid for self-directed treatment.
Calculate body surface area
Body surface area is a modelled estimate of skin surface derived from height and weight. Direct measurement of every contour is impractical in routine care, so published equations approximate BSA from the two easy anthropometrics. Adults and children both appear in the clinical literature; the formulas offered here are the common named regressions used in practice and teaching.
Mosteller is the default because it is simple and widely used at the bedside. Du Bois and Du Bois (1916) is the classic alternative. Haycock and Gehan-George are additional published options the calculator reports so disagreement across methods stays visible. Results appear in square metres, typically near 1.5 to 2.2 m² for many adults.
The Body Surface Area Calculator provides a general geometric estimate for information and learning. It does not recommend a drug dose, a fluid rate or a treatment plan. When BSA is used clinically, the clinician selects the formula, checks the inputs and owns the decision.
Choose a BSA formula
Four named equations are available, each taking height in centimetres and weight in kilograms and returning surface area in square metres. Comparing them side by side shows how closely everyday adult inputs usually agree, and where institutional protocols still insist on one named form over the calculator's educational default.
Mosteller (1987) `` BSA = √(height_cm × weight_kg / 3600) ``
Du Bois and Du Bois (1916) `` BSA = 0.007184 × height_cm^0.725 × weight_kg^0.425 ``
Haycock (1978) `` BSA = 0.024265 × height_cm^0.3964 × weight_kg^0.5378 ``
Gehan and George (1970) `` BSA = 0.0235 × height_cm^0.42246 × weight_kg^0.51456 ``
Source: Mosteller 1987, Du Bois and Du Bois 1916, Haycock 1978, Gehan and George 1970, as listed in the site health reference. For many ordinary adult heights and weights the four results cluster tightly. Larger gaps can appear at extremes of size, which is one reason clinical protocols specify which equation to use.
Mosteller's square-root form is easy to compute by hand and is the most common clinical default noted in the reference data. Du Bois remains deeply embedded in older literature and some institutional protocols. Haycock and Gehan-George appear when a service standard names them. This tool does not choose a protocol for a hospital; it shows the arithmetic so the differences are inspectable. Rounding to two decimals is enough for education; clinical charts may carry more precision or different rounding rules.
Calculate BSA with the Mosteller formula
A concrete adult example makes the Mosteller square-root steps easy to verify by hand or on a phone. Take a person 180 cm tall weighing 80 kg, which is the fixture used to check the default path in the calculation engine.
1. Multiply height by weight. 180 × 80 = 14,400
2. Divide by 3600. 14,400 / 3600 = 4
3. Take the square root. √4 = 2.0 m²
So Mosteller returns 2.0 m² for these inputs. The same person under the other equations yields approximately 2.00 m² (Du Bois), 2.01 m² (Haycock) and 2.01 m² (Gehan-George). Agreement this close is common near average adult size; it is less guaranteed at the tails of height or weight.
Work the steps with a phone calculator if verifying by hand, and confirm that height really is in centimetres and weight in kilograms before trusting the square root. Mixing inches or pounds into a centimetre-kilogram formula silently wrecks the result. When US units are entered on the page, conversion happens first; the printed breakdown should still be checked if the number will be discussed with a clinician.
Understand how BSA is used clinically
In oncology and other specialties, many drug doses are ordered per square metre so people of different sizes receive proportional exposure under a protocol. Cardiac index divides cardiac output by BSA to normalise flow to body size. Burn care and some paediatric calculations also reference surface area. Those workflows assume trained staff, verified measurements, approved equations and monitoring for effect.
None of that workflow is something a public calculator should invite users to complete alone. Chemotherapy and similar agents have narrow margins. A centimetre error in height, a stale weight, or the wrong equation relative to a protocol can matter. The educational value of seeing Mosteller equal 2.0 m² for 180 cm and 80 kg is real. Translating that into a milligram dose at home is not.
The result block on this page always carries a clinical deferral: BSA may be used in dosing and related decisions, and those decisions belong with a clinician. The figure is for understanding the measurement. It is not medical advice and not a dosing tool for self-use. If a care team has already quoted a BSA, ask which formula they used rather than substituting a different web default without discussion.
Amputees, people with substantial oedema, and some other clinical situations need adjusted approaches that plain height-weight equations do not capture. Those adjustments are always clinical judgements made carefully at the bedside. The public tool still shows the unadjusted named formulas so the standard arithmetic is transparent, while remaining clear that special cases belong in clinic, not in a browser worksheet.
What if a published protocol uses a different equation than Mosteller? Follow the protocol. Educational defaults on a website do not override a hospital formulary, an oncology pathway or a paediatric service standard. The comparison table exists so a reader can see how far an alternate formula would have moved the square-metre figure, then take that observation back to the clinical conversation rather than acting on it alone.
Frequently asked questions
What is a typical adult BSA?
Many adults fall roughly between about 1.5 and 2.2 m², with wider values at the extremes of height and weight. The worked example of 180 cm and 80 kg gives 2.0 m² by Mosteller. Typical is a description of common results, not a health target.
Why is Mosteller the default?
Mosteller is simple, widely taught and commonly used clinically for that practicality. The site health reference notes it as the most common clinical choice among the options listed. Protocols may still require Du Bois or another named equation.
Do the formulas always agree?
Near average adult size they often agree within a few hundredths of a square metre. At very high or low weight for height, gaps widen. When a clinical protocol names a formula, that named formula wins over a web default.
Can this calculator be used to dose medication?
No. The tool computes an educational BSA only. Medication dosing, including chemotherapy, must be performed by qualified clinicians under appropriate protocols. Do not adjust prescribed doses from a website estimate.
What units does the calculator need?
The published equations use centimetres and kilograms. US height and weight entries are converted before substitution. Confirm the converted values if checking the arithmetic by hand.
Is BSA the same as BMI?
No. BMI is weight divided by height squared and is used in weight-category screening. BSA estimates surface area in square metres for size-normalised clinical calculations. They answer different questions.
Does sex change the BSA formula?
The four equations implemented here use height and weight only; they do not include a sex coefficient. Some research models differ, but this page stays with the named formulas in the health reference.
Why must a clinician interpret BSA?
Because the number is usually a step toward a medical decision with real risk if misapplied. A clinician combines BSA with diagnosis, labs, protocol rules and monitoring. A standalone square-metre figure cannot carry that responsibility.
How often should height and weight be updated for BSA?
Clinically, weight can change during treatment and height should be measured rather than recalled. For education, any consistent pair of measurements is fine; for care, follow the clinic's measurement protocol.
What about children?
Paediatric dosing and BSA use careful institutional rules and often age-specific practice. This page can still compute the named adult-published equations from height and weight for learning, yet paediatric treatment decisions remain entirely with the clinical team.
Does clothing or time of day change BSA?
Height is stable in adults; weight shifts with food, fluid and clothing. Clinical measurements use a consistent method. For education, small weight changes move BSA only slightly near the Mosteller square root, but dosing contexts still require the clinic's measured values.
Summary
The Body Surface Area Calculator estimates BSA in square metres from height and weight using Mosteller by default, with Du Bois, Haycock and Gehan-George available for comparison. For 180 cm and 80 kg, Mosteller returns 2.0 m². BSA is used clinically in contexts such as drug dosing and cardiac index, yet this page computes the educational number only.
Interpretation and any dosing decision belong with a qualified clinician; the estimate is general information, not a treatment tool.