Estimate body surface area (BSA) in square meters using the Mosteller, Du Bois & Du Bois, and Haycock formulas — supports metric (cm/kg) and imperial (ft/in, lbs). Compare all three formulas side by side. Educational estimate only — not for real medical dosing.
📏 All three formulas use height in centimeters and weight in kilograms internally. Switch to Imperial to enter feet/inches and pounds — the calculator converts them automatically.
⚠️ Educational estimate only. This tool is not a substitute for clinical judgment. Actual medical or drug dosing calculations — including chemotherapy dosed per m² BSA — must always be performed and verified by a licensed physician or pharmacist. Never use this calculator to determine or adjust a real medication dose.
Enter height and weight to estimate body surface area
This body surface area (BSA) calculator estimates the total surface area of the human body, in square meters, from height and weight — a value clinicians use far more often than most people realize. Rather than relying on a single equation, this free BSA calculator computes results using three widely referenced formulas — Mosteller (the modern clinical default), Du Bois & Du Bois (the 1916 original), and Haycock (best validated for infants and children) — and shows them side by side so you can see how closely they agree. It fully supports both metric (cm/kg) and imperial (ft/in, lbs) units, converting internally so the underlying math is identical regardless of which units you enter.
Body surface area is a calculated estimate of the total external area of the human body, expressed in square meters (m²). Because directly measuring the surface area of a living person is impractical, researchers over the past century have developed regression formulas that predict BSA from just height and weight, calibrated against a handful of studies that did measure surface area directly. This calculator applies three of the most cited of those formulas, letting you compare their outputs rather than relying on just one.
This tool is built for students, nurses, caregivers, and curious patients who want to understand how a BSA figure is derived — for example, after seeing "m²" referenced on a lab report, a chemotherapy protocol summary, or a pediatrician's growth chart. It is not a replacement for the BSA calculation a hospital pharmacy or oncology team performs when preparing an actual medication dose, and it should never be used for that purpose.
BSA correlates more closely with metabolic rate, blood volume, and cardiac output than body weight alone does, which is why it shows up across so many corners of medicine: chemotherapy and other drug dosing, burn injury fluid resuscitation, cardiac index calculations in critical care, kidney function (GFR) normalization to a standard 1.73 m², and even nutrition and metabolic research. Understanding roughly how BSA is calculated — and that three independently derived formulas land within a tight range of each other for the same person — builds useful health literacy without requiring a medical degree.
This calculator provides an educational estimate only. It is not a diagnostic or prescribing tool. Actual medical or drug dosing calculations — including chemotherapy dosed per m² of BSA — must always be performed and independently verified by a licensed physician or pharmacist using validated clinical software and current patient data. Never use this page, or any online calculator, to calculate or adjust a real medication dose.
Exactly how this calculator converts height and weight into a body surface area estimate
All three results are rounded to two decimal places. Because the formulas were each independently derived and calibrated, they typically agree within a few hundredths of a square meter for a normal adult — a useful sanity check that no value was mistyped.
Published by Dr. R.D. Mosteller as a simpler alternative to Du Bois, using only a square root instead of fractional exponents. It is the most widely used formula in modern clinical practice and the default in most electronic health record systems today.
The original BSA formula, derived by directly measuring the surface area of just nine people and fitting a power-law regression to height and weight. It remains a historical and reference standard, though it has largely been superseded by Mosteller for routine clinical use.
Derived using data spanning a wide weight range, including infants and children, which makes it the formula most commonly recommended for pediatric and neonatal BSA-based dosing calculations.
From entering height and weight to comparing all three BSA formulas
Pick Metric (cm/kg) or Imperial (ft/in, lbs) depending on which units you have available. You can switch at any time — values convert automatically.
Type your height into the corresponding field, measured standing straight without shoes for the most accurate reading.
Type your current body weight into the weight field.
Choose Mosteller (default, most common in adult clinical use), Du Bois & Du Bois (classic historical formula), or Haycock (best for infants and children) as your primary formula.
See your BSA in m² from all three formulas side by side, plus a comparison bar chart. Remember this is an educational estimate — actual medical dosing must be verified by a licensed physician or pharmacist.
Using the calculator's own default scenario — 170 cm tall, 70 kg
A person is 170 cm tall and weighs 70 kg. Let's calculate BSA using all three formulas.
Explanation: All three formulas land in a tight 1.81–1.83 m² range for the same person — a difference of only 0.02 m², or roughly 1%. This consistency is exactly why Mosteller is trusted as the modern clinical default: it produces essentially the same answer as the more complex power-law formulas while being far simpler to calculate by hand. If a real BSA-based drug dose were being calculated from these numbers, a physician or pharmacist would still independently verify the figure using validated clinical software before administering anything.
Typical BSA ranges and where they show up in clinical practice
| BSA Range (m²) | Typical Population | Common Clinical Context |
|---|---|---|
| 0.25–0.5 | Newborns and young infants | Neonatal drug dosing (Haycock preferred) |
| 0.9–1.3 | Young children (roughly 5–10 years) | Pediatric chemotherapy and drug dosing |
| 1.4–1.6 | Small-frame or petite adults | General dosing reference, cardiac index baseline |
| 1.6–1.9 | Average adult women | Chemotherapy dosing, eGFR normalization (1.73 m² standard) |
| 1.9–2.1 | Average adult men | Chemotherapy dosing, burn fluid resuscitation calculations |
| 2.2+ | Large-frame or tall adults | Dose-capping considerations, ECMO/bypass circuit sizing |
Chemotherapy and drug dosing: many cancer drugs and some other medications are dosed as milligrams per square meter of BSA (mg/m²) rather than by weight alone, because BSA tracks metabolic rate and blood volume more consistently across different body sizes.
Burn injury assessment: the percentage of total body surface area burned (%TBSA) is combined with a patient's total BSA to estimate fluid resuscitation volumes using protocols like the Parkland formula.
Cardiac index: dividing cardiac output by BSA (Cardiac Output ÷ BSA) gives a size-adjusted measure of heart performance used in critical care and cardiology.
This result is for informational and educational purposes only and is not a medical diagnosis or a real drug dose. BSA formulas are population-calibrated estimates — they do not know your medical history, organ function, or the specific drug protocol a clinician would use.
This calculator provides educational estimates only and must never be used to calculate or adjust a real medication dose. Actual clinical and drug dosing calculations — including chemotherapy dosed per m² BSA — must always be performed and verified by a licensed physician or pharmacist.
Where body surface area shows up in medicine, research, and education — always as reference, never as a replacement for professional calculation
Understand how oncology teams reference BSA (mg/m²) when explaining a treatment plan — the actual dose is always calculated and verified by the clinical team.
See why the Haycock formula is specified in many pediatric dosing protocols and growth-related calculations.
Understand how total BSA combines with the Rule of Nines to estimate fluid resuscitation needs after a burn injury.
Learn how Cardiac Output ÷ BSA is used in critical care to compare heart performance across patients of different sizes.
See why GFR is reported per 1.73 m² and pair this tool with NeftCal's GFR Calculator for kidney function context.
Understand why BSA is one of the variables clinical teams reference when sizing extracorporeal circuits.
Some historical metabolic rate equations normalize energy expenditure per unit of body surface area rather than per kilogram.
Understand how early-phase drug trials often use BSA-based dosing to scale doses safely across participants.
Some radiotracer dosing protocols reference body surface area alongside weight-based calculations.
Students can use the worked formulas to understand how a BSA figure on a chart or protocol was derived.
Understand the "m²" figure referenced on a lab report, prescription, or pediatrician's chart without needing a medical degree.
Compare the century-old Du Bois formula against the modern Mosteller and pediatric-focused Haycock formulas side by side.
What this BSA calculator does well, and where it can't replace professional clinical calculation
A quick reference for which formula clinicians and researchers most often reach for in each context
| Formula | Preferred Clinical Context | Notes |
|---|---|---|
| Mosteller | General adult clinical use, most electronic health record systems | Simplest calculation, widely used default today |
| Du Bois & Du Bois | Historical reference, some older or protocol-specified calculations | Original 1916 formula, derived from just nine subjects |
| Haycock | Infants, children, and pediatric dosing calculations | Best validated across a wide pediatric weight range |
Summary: This free BSA calculator gives you an instant, side-by-side comparison of the Mosteller, Du Bois, and Haycock formulas in metric or imperial units — a useful educational reference, not a substitute for clinical calculation. Pair it with related tools like the GFR Calculator and BMI Calculator for a fuller picture of clinical body-metric tools.
Common questions about body surface area calculations
Official guidance to complement this calculator — not a substitute for licensed medical advice
Explore other health and clinical reference tools