What is body surface area and why does it matter?

Body surface area (BSA) is the total surface area of the human body, expressed in square metres. It tracks metabolic mass better than weight alone, so clinicians scale many things to it: chemotherapy doses, the cardiac index, glomerular filtration rate, and burn assessment. An average adult sits around 1.7 m². A 170 cm, 70 kg person is about 1.82 m² by the Mosteller formula. It is a model, not a measurement, which is why several formulas exist.

How does the Mosteller formula work?

Mosteller (1987) is the simplest and most widely used: BSA equals the square root of height in cm times weight in kg, divided by 3600. For 170 cm and 70 kg that is the square root of (170 times 70 over 3600), which is the square root of 3.305, about 1.82 m². It is popular precisely because you can do it on any calculator without exponents, and it agrees closely with the older, more elaborate formulas for adults.

Why do the four formulas give slightly different answers?

Each formula was fitted to a different group of people. DuBois & DuBois (1916) used just nine subjects. Gehan & George (1970) refit the curve to 401 people. Haycock (1978) validated theirs down to premature newborns. Mosteller (1987) is an algebraic shortcut. For a 170 cm, 70 kg adult they land at 1.82, 1.81, 1.83 and 1.83 m², within about 0.03 of each other. The differences grow at very low or very high body sizes, which is exactly where seeing all four side by side helps.

Is BSA used for chemotherapy dosing?

Yes. Many cytotoxic drugs are dosed in milligrams per square metre of BSA, so a 1.8 m² patient on a 75 mg/m² regimen receives 135 mg. Most oncology pharmacies use the Mosteller formula for this. This calculator can show you the number, but it must never be used to set a real dose. Actual dosing accounts for capping, rounding, organ function, and clinical judgement, and is the job of a qualified prescriber and pharmacist.

What is the difference between BSA and BMI?

BMI (weight divided by height squared) is a single ratio meant to flag under or over weight relative to height. BSA estimates an actual physical area in square metres and is used to scale physiological quantities and drug doses. A 170 cm, 70 kg person has a BMI of about 24.2 and a BSA of about 1.82 m². BMI answers is this body too heavy for its height, BSA answers how much surface and metabolic mass is there to dose against. If you want BMI, our BMI calculator is one click away.

Is this calculator private and accurate?

Every formula runs as plain JavaScript inside your browser tab. No height, weight, or result is ever sent to a server, and there is no logging of what you enter. The formula constants are taken directly from the original papers, so the numbers match a clinical reference for the typical adult range. The one caveat is the share link: it encodes your height and weight in the URL, so do not paste a share link containing real patient data into a public channel.

Cross-check a clinical reference BSA

A nursing student or pharmacy tech learning oncology math wants to confirm a worked example from a textbook. Enter the patient height and weight, and the Mosteller column should match the answer key while the other three formulas sit a hair above or below. Seeing the spread is the lesson: the textbook used Mosteller, but DuBois would have given a slightly different milligram count.

Compare formulas for a paediatric case

BSA formulas were fitted on different populations and diverge most in children. Plug in a 100 cm, 16 kg child and watch Haycock, validated down to newborns, line up against Mosteller. The side-by-side view makes a textbook point concrete instead of abstract: which formula to trust depends on who it was built for.

Estimate cardiac index for a physiology homework problem

Cardiac index is cardiac output divided by BSA. For a homework problem giving height, weight, and cardiac output, compute BSA here first, then divide. Using all four formulas shows how much the index shifts depending on which BSA you pick, which is exactly the kind of sensitivity question a good physiology course asks.

Build intuition for the 1.7 m squared average

Most dosing nomograms quote a 1.73 m² standard body. Try a few common heights and weights and you will see when a person lands near, above, or below that reference. It turns a memorized constant into something you can feel, which is the whole point of an education tool.

Body Surface Area (BSA) Calculator — Mosteller, DuBois, Haycock, Gehan-George

Four formulas side by side — Mosteller, DuBois, Haycock, Gehan-George — cm/kg or in/lb, one-click copy, browser-only

Runs locally
Category Calculator
Best for Getting a realistic range before a purchase, plan, workout, or schedule decision.

For education and reference only. This is not medical advice. Clinical dosing must be done by a qualified professional with the patient in front of them.

Height

Weight

Formula	BSA (m²)
Mosteller	1.82
DuBois	1.81
Haycock	1.83
Gehan-George	1.83

BSA is widely used to normalize chemotherapy doses, set the cardiac index, and scale renal clearance.

What this tool does

A free body surface area calculator that runs four published BSA formulas at once so you can compare them instead of trusting a single number. Enter height and weight and the tool returns the Mosteller value (the square root of height times weight over 3600), alongside the DuBois & DuBois, Haycock, and Gehan & George estimates, all in square metres. Switch between metric (cm/kg) and imperial (in/lb) without retyping. BSA is the figure clinicians use to normalize chemotherapy doses, set the cardiac index, and scale renal clearance, so seeing the spread between formulas matters: for a typical adult the four agree to within about 0.03 m², but the gap widens at the extremes of body size. Everything is computed in your browser, nothing is uploaded, and the share link reproduces your exact inputs. This is an education and reference tool, not medical advice.

Tool details

Input: Numbers; The page exposes text boxes, numeric controls, file pickers, or structured inputs depending on the tool.
Output: Live result + Copy; The result area focuses on usable output, with copy, download, or preview actions when supported.
Privacy: Browser-side processing; The main tool logic does not call an external API, so inputs normally stay in the current tab.
Save / share: Shareable URL state; Key settings are encoded in the URL so another person can reopen the same setup.
Performance budget: Initial JS <= 9 KB; No WASM budget is declared, keeping the tool quick to open on mobile.
Best fit: Calculator · Student; Category and role tags drive related tools, internal links, and quick fit checks.

How to use

1. Input

Paste or drop your content into the tool panel.
2. Process

Click the button. All processing is local in your browser.
3. Copy / Download

Copy the result or download to disk in one click.

How Body Surface Area (BSA) Calculator fits into your work

Use it for fast estimates, comparisons, and planning numbers before you make the final call.

Calculation jobs

Getting a realistic range before a purchase, plan, workout, or schedule decision.
Comparing scenarios by changing one input at a time.
Turning rough assumptions into a number you can discuss.

Calculation checks

Double-check units, dates, rates, and rounding assumptions.
Treat health, finance, tax, and legal outputs as planning aids, not professional advice.
Save the inputs that produced an important result so you can reproduce it later.

Good next steps

These links move the current task into a more complete workflow.

Real-world use cases

Cross-check a clinical reference BSA
A nursing student or pharmacy tech learning oncology math wants to confirm a worked example from a textbook. Enter the patient height and weight, and the Mosteller column should match the answer key while the other three formulas sit a hair above or below. Seeing the spread is the lesson: the textbook used Mosteller, but DuBois would have given a slightly different milligram count.
Compare formulas for a paediatric case
BSA formulas were fitted on different populations and diverge most in children. Plug in a 100 cm, 16 kg child and watch Haycock, validated down to newborns, line up against Mosteller. The side-by-side view makes a textbook point concrete instead of abstract: which formula to trust depends on who it was built for.
Estimate cardiac index for a physiology homework problem
Cardiac index is cardiac output divided by BSA. For a homework problem giving height, weight, and cardiac output, compute BSA here first, then divide. Using all four formulas shows how much the index shifts depending on which BSA you pick, which is exactly the kind of sensitivity question a good physiology course asks.
Build intuition for the 1.7 m squared average
Most dosing nomograms quote a 1.73 m² standard body. Try a few common heights and weights and you will see when a person lands near, above, or below that reference. It turns a memorized constant into something you can feel, which is the whole point of an education tool.

Common pitfalls

Mixing units. Entering height in inches while the field is set to cm makes the BSA absurdly small. Pick metric or imperial first, then read the suffix on each field before you type.
Treating BSA as a measured value. It is a statistical estimate from height and weight, accurate to a few percent for typical adults but less so at the extremes. Two people of the same height and weight always get the same BSA here, even though their real surface areas differ.
Using any number from this tool to set a real drug dose. Clinical dosing involves capping, rounding, organ function, and a prescriber. This calculator is for learning the formulas, not for treating a patient.

Privacy

All four formulas run as plain JavaScript inside your browser tab. No height, weight, or result ever leaves the page, and nothing is logged. The one caveat is the share link, which encodes your height and weight in the URL query string, so a link pasted into chat will record those values in the recipient server access log. Do not share a link that contains real patient data; use the copy button and paste the text instead.

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Body Surface Area (BSA) Calculator — Mosteller, DuBois, Haycock, Gehan-George

What this tool does

Tool details

How to use

1. Input

2. Process

3. Copy / Download

How Body Surface Area (BSA) Calculator fits into your work

Calculation jobs

Calculation checks

Good next steps

Real-world use cases

Cross-check a clinical reference BSA

Compare formulas for a paediatric case

Estimate cardiac index for a physiology homework problem

Build intuition for the 1.7 m squared average

Common pitfalls

Privacy

FAQ

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