Instantly calculate BSA in m² using Mosteller, Du Bois, Haycock, and Gehan & George formulas — used for chemotherapy dosing, cardiac index, and burn assessment.
Results update live as you type.
Body Surface Area (Mosteller)
Average (4 formulas)
1.91
m²
Typical adult
1.9
men · 1.6 women
Cardiac index ref
4.8 – 7.7
L/min @ CI 2.5–4.0
Variance
±0.02
between formulas
| Group | Typical BSA (m²) | Notes |
|---|---|---|
| Newborn | 0.20 – 0.30 | Paediatric |
| Child (9 yrs) | 1.05 – 1.10 | Paediatric |
| Adult woman | 1.50 – 1.70 | Average |
| Adult man | 1.80 – 2.00 | Average |
| Large adult | 2.00 – 2.40 | Above average |
| Very large adult | 2.40 + | Outlier |
The Formulas
Body Surface Area is derived from height and weight using empirically-fit equations. The Mosteller formula (1987) is the simplest and the most widely used in clinical practice today. Du Bois & Du Bois (1916) is the historical reference still used in many drug-dosing guidelines. Haycock (1978) is preferred for paediatric patients, and Gehan & George (1970) was derived from a larger sample.
Mosteller formula
About This Tool
A body surface area calculator — also called a BSA calculator — is a free clinical tool that estimates the total surface area of a person's body in square metres. BSA is used by clinicians for chemotherapy dosing, calculating cardiac index, indexing kidney function, and assessing the percentage of body surface affected by burns.
This online BSA calculator applies four clinically-recognised formulas — Mosteller, Du Bois & Du Bois, Haycock, and Gehan & George — so you can compare results across the equations your clinician or institution prefers. The Mosteller formula is the most widely used today because it is simple to compute mentally and produces values within a few percent of the more complex equations.
BSA correlates with metabolic mass, blood volume, and organ size more reliably than weight alone, which is why drugs with narrow therapeutic windows — particularly cytotoxic chemotherapy agents — are usually dosed per square metre rather than per kilogram. It is not, however, a substitute for clinical judgement, and BSA-based dosing is increasingly being refined for obese patients and the elderly.
Use this free BSA calculator in metric or US imperial units. All calculations run entirely in your browser — no sign-up, no data collected, no medication should be self-administered based on the result.
Four Formulas
Mosteller, Du Bois, Haycock, and Gehan & George computed side-by-side in m².
Metric & Imperial
Switch between US (lbs, ft/in) and metric (kg, cm) with one click.
Visual Comparison
A bar chart shows where each formula lands, so you can see the variance at a glance.
Live Calculation
BSA updates in real time as you type or drag a slider — no submit button needed.
100% Free & Private
No account, no tracking — every calculation runs locally in your browser.
Reference Ranges
Compare your BSA against newborn, paediatric, and adult reference bands.
Two inputs give you BSA from four formulas in seconds.
Toggle between US / Imperial (feet, inches, pounds) and Metric (centimetres, kilograms). The calculator converts to cm and kg internally — pick whichever unit you have handy.
Type your height directly. For imperial, fill in feet and inches separately. For metric, just enter your height in centimetres. Accuracy matters — a few centimetres changes BSA by ~0.05 m².
Add your current weight (pounds or kilograms). Drag the slider to see how BSA changes with weight. For clinical use, prefer actual body weight rather than ideal or adjusted weight unless your protocol specifies otherwise.
Provide your age and biological sex. These don't change the BSA number itself but help the calculator flag whether you sit in the typical adult range or a paediatric / very-large band.
Your Mosteller BSA headlines the result, with Du Bois, Haycock, and Gehan & George values shown beneath. The bar chart visualises agreement between formulas.
Compare your number against the reference table to see whether you fall in the average adult, large adult, or paediatric band. Never self-dose medication from this value — drug dosing must be performed by qualified medical professionals.
Everything you need to know about Body Surface Area, the formulas, and how to interpret your result.
Body Surface Area (BSA) is the calculated total surface area of a person's body, expressed in square metres (m²). It is derived from height and weight using empirically-fit equations. BSA is used in clinical medicine for chemotherapy dosing, calculating cardiac index, indexing renal function (eGFR), and estimating fluid replacement in burn patients. The average adult BSA is around 1.9 m² for men and 1.6 m² for women.
The simplest and most widely used formula is the Mosteller formula: BSA (m²) = √((height in cm × weight in kg) ÷ 3600). So a person 175 cm tall weighing 75 kg has a BSA of √((175 × 75) ÷ 3600) = √3.645 = 1.91 m². This calculator also computes Du Bois, Haycock, and Gehan & George values for comparison.
It depends on your context. The Mosteller formula is the most widely used in modern clinical practice because it is mentally calculable and produces values within ~2% of more complex equations. Du Bois & Du Bois (1916) is the historical reference and is still embedded in many drug-dosing tables. Haycock (1978) is preferred for paediatric and obese patients. Gehan & George (1970) was derived from the largest sample of the four. For most adults the four values agree to within 0.03 m².
Average BSA for adults is approximately 1.9 m² for men and 1.6 m² for women. Newborns are around 0.25 m², a 2-year-old around 0.5 m², a 9-year-old around 1.07 m², and a 13-year-old around 1.33 m². These reference values are widely used in paediatric drug dosing.
Chemotherapy agents have narrow therapeutic windows — small dose changes can dramatically alter both efficacy and toxicity. BSA correlates with blood volume, cardiac output, glomerular filtration rate, and metabolic rate more reliably than weight or age alone, so dosing per m² produces more consistent drug exposure across patients of different builds. The convention dates back to early oncology trials and is still standard practice — although alternative strategies (flat dosing, AUC-based dosing) are increasingly used for specific agents.
No. BMI (Body Mass Index) is the ratio of weight to height squared (kg/m²) and is used to screen for underweight, healthy weight, overweight, and obesity. BSA (Body Surface Area) is the calculated total skin surface of the body in m² and is used for drug dosing and physiologic indexing. They use the same two inputs but answer entirely different clinical questions and are not interchangeable.
Burn extent is expressed as a percentage of Total Body Surface Area (TBSA) affected. Clinicians estimate this percentage at the bedside using the Rule of Nines (each arm 9%, each leg 18%, anterior trunk 18%, etc.) or the more accurate Lund-Browder chart for paediatric patients. A calculated BSA helps determine fluid resuscitation volumes using formulas such as Parkland (4 mL × kg × %TBSA over 24 hours).
Yes — the same equations apply. The Haycock formula was specifically validated against paediatric direct-measurement data and is the preferred choice for infants and children at many institutions. For neonates BSA tends to be in the 0.2–0.3 m² range; for a 1-year-old around 0.45 m². As always, paediatric drug dosing must be performed by a qualified clinician.
BSA equations were derived from samples that did not include many morbidly obese subjects, so calculated BSA can over-estimate effective surface area in very high BMI patients. For oncology dosing this has led to capping practices (e.g. capping BSA at 2.0 m² or using adjusted body weight) at some centres, although evidence supports full-weight dosing in many regimens. Always follow institutional protocols.
No — never. This BSA calculator is provided for educational and reference purposes only. Drug dosing — particularly chemotherapy, anaesthetic, and cardiac medications — must be calculated, prescribed, and verified by qualified medical professionals using validated clinical systems. Self-medicating based on a calculated BSA is dangerous and may be fatal.
The Du Bois & Du Bois formula (1916) was the original and used for most of the 20th century: BSA = 0.007184 × height0.725 × weight0.425. The Mosteller formula (1987) is a much simpler square-root expression that agrees with Du Bois to within ~2% for most adults and is now the preferred default in many clinical and research settings. For very small children or very obese adults the two can diverge slightly.
The math is exact — this calculator applies each published formula precisely and produces results accurate to two decimal places for the height and weight you provide. Real-world accuracy depends on the quality of your measurements: measure height with shoes off against a wall, and weigh on a calibrated scale wearing minimal clothing. This calculator is intended for educational and screening use and is not a substitute for medical advice or institution-validated clinical software.