Body Surface Area Calculator

Body surface area (BSA) is the total surface area of the human body, expressed in square meters. For a 5′9″ (175 cm), 160 lb (72.6 kg) adult, the Du Bois formula gives a BSA of about 1.88 m², while the Mosteller formula gives essentially the same 1.88 m² - within a fraction of a percent of each other. That close agreement is typical, and it is exactly why both formulas are trusted in clinical settings. This BSA calculator shows them side by side so you can see the small differences for your own measurements.

Doctors often prefer BSA over body weight because it tracks better with metabolic rate, blood volume and organ size. That makes it the standard for chemotherapy dosing, calculating cardiac index, and estimating fluids in burn patients.

The BSA formulas

The historic and most-cited method is the Du Bois & Du Bois formula:

A simpler and extremely popular alternative is the Mosteller formula, which is easy to compute by hand:

This tool also reports the Haycock (often used for children) and Gehan-George formulas, then averages all four so you can see a consensus value. Every formula uses metric units internally, so your imperial pounds and feet/inches are converted first.

What is a normal BSA?

There is no rigid cutoff, but most adults land between roughly 1.5 and 2.0 m². The widely-used reference value is about 1.73 m² for an average adult - for instance, kidney function (GFR) is conventionally normalized to 1.73 m². Children have a much smaller BSA relative to their weight, which is one reason pediatric dosing depends so heavily on accurate surface-area estimates.

Where BSA is actually used

• Chemotherapy dosing: many cancer drugs are prescribed in mg per m² of BSA.
• Cardiac index: cardiac output divided by BSA, to compare hearts across body sizes.
• Burn care: fluid resuscitation and burn extent reference body surface.
• Kidney function: GFR is normalized to a standard 1.73 m² BSA.

Because dosing protocols sometimes cap BSA (commonly at 2.0 m²) or adjust for body composition, the number from any online calculator is a starting estimate only.

How to use this BSA calculator

You only need two measurements - height and weight. Work through the calculator in order:

1. Pick your units: leave it on imperial to enter feet/inches and pounds (the US default), or switch to metric for centimeters and kilograms. The result is identical either way because everything is converted to kg and cm internally.
2. Enter your height: type your height in the selected unit. For imperial, use the feet and inches fields together (for example 5 ft 9 in).
3. Enter your weight: use a recent, accurate figure. Even a few pounds changes the BSA slightly, so use scale weight rather than a rough guess.
4. Read the results: the calculator shows the Du Bois, Mosteller, Haycock, and Gehan-George values in m² plus their average. Compare them - they should land within a couple of percent of each other.

There is nothing to submit; the values update instantly as you type. If a number looks far too large or small, double-check that the right unit toggle is selected.

Who this calculator is for

BSA matters to more people than just oncologists. This tool is useful for:

• Patients and caregivers who have heard a dose described "per square meter" and want to understand the number behind it.
• Nursing and pharmacy students checking their hand calculations against multiple formulas.
• Clinicians who want a quick cross-check of Du Bois against Mosteller, Haycock, and Gehan-George.
• Researchers normalizing physiological measurements - like cardiac output or GFR - to body size.
• Anyone curious about how surface area scales with height and weight compared with simpler measures like BMI.

Worked example: comparing all four formulas

Take a person who is 5′6″ (168 cm) and 140 lb (63.5 kg). Running the numbers gives:

• Du Bois: about 1.72 m²
• Mosteller: about 1.72 m²
• Haycock: about 1.72 m²
• Gehan-George: about 1.73 m²

The four results cluster within roughly 1% - landing essentially on the classic 1.73 m² reference value. This tight agreement is the whole point: it means a clinician can pick one formula and trust it, and it is why a difference of more than a few percent between formulas usually signals a data-entry error (such as a unit mix-up) rather than a real disagreement.

Key terms explained

• Body surface area (BSA): the total external surface of the body in m². It grows with both height and weight, so it captures overall body size better than weight alone.
• Cardiac index: cardiac output divided by BSA. Indexing to BSA lets doctors compare a small and a large person's heart performance fairly.
• GFR (glomerular filtration rate): a measure of kidney function conventionally reported per 1.73 m² of BSA, so results are comparable across body sizes.
• Du Bois exponents: the powers 0.425 (weight) and 0.725 (height) in the Du Bois formula, fitted to early surface-area measurements.
• Dose banding / capping: rounding BSA into bands or limiting it (often at 2.0 m²) to standardize and cap drug doses in some protocols.

BSA vs. BMI: what is the difference?

Both BSA and BMI combine height and weight into a single number, but they answer different questions. BMI (weight ÷ height²) is a screening proxy for whether someone is under- or over-weight relative to height, and it has fixed category cutoffs (for example, 18.5-24.9 is "normal"). BSA, by contrast, estimates physical surface area and has no "healthy range" - a larger BSA simply means a larger body, not a better or worse one. Clinicians reach for BMI to talk about weight status and risk, and for BSA to scale doses and physiological measurements to body size. If you are interested in weight relative to height, the BMI Calculator and Ideal Weight Calculator are the right tools; BSA answers a separate, dosing- and physiology-focused question.

The four formulas compared

This calculator runs four published formulas at once. They were each fitted to different study populations, which is why they exist side by side rather than one replacing the others:

• Du Bois & Du Bois (1916): the original and most-cited formula, derived from just nine subjects (one of whom was a child with measured surface area). It uses two separate exponents and remains the historic reference, but its tiny sample is a known weakness.
• Mosteller (1987): a single square-root formula designed to be computed quickly by hand or on a basic calculator. Its simplicity made it the de-facto standard in modern oncology, and it agrees with Du Bois to within roughly 1-2% for most adults.
• Haycock (1978): developed and validated against infants and children, so it is the formula of choice when surface area is needed for a pediatric patient. It tends to track the others closely for adults too.
• Gehan & George (1970): fitted to a much larger dataset of 401 direct measurements across all ages, which gives it broad coverage. It is less famous than Du Bois or Mosteller but is statistically well-grounded.

By showing all four plus their average, the tool turns "which formula should I use?" into a non-issue for most people: when the values cluster tightly, any of them is a safe estimate. A wide spread, on the other hand, is a red flag that your height or weight entry is off.

How BSA scales with height and weight

BSA does not grow in a straight line with either measurement. Because the Du Bois exponents are 0.425 for weight and 0.725 for height, height has a noticeably larger effect on surface area than weight does, pound for pound. In practical terms, a tall, slim person and a shorter, heavier person can share almost the same BSA even though they look very different and have very different BMI values. This is the core reason BSA is useful: it captures overall body size in a way that a single weight reading cannot, while still being far simpler to obtain than a direct measurement.

The diminishing-returns shape also explains the dosing caps you sometimes hear about. Doubling a person's weight does not double their surface area, so naively scaling a drug dose by weight would over-dose larger patients. Scaling by BSA softens that, and capping BSA (often at 2.0 m²) softens it further at the extreme end.

BSA, BMI and body composition together

BSA, BMI and body-composition tools each answer a different question, and they are most useful read together rather than in isolation:

• BSA tells you how large the body is overall, for scaling doses and physiological measurements.
• BMI tells you whether weight is high or low relative to height, as a quick health-risk screen - calculate it with the BMI Calculator.
• Body composition tells you how much of that weight is fat versus lean tissue, which the height-and-weight formulas cannot see. For that, use the Body Fat Calculator or the Lean Body Mass Calculator.

For example, two people with identical BSA might have very different body-fat percentages; BSA alone treats them the same. If your underlying goal is fitness or metabolic planning rather than dosing, a BMR Calculator or Calorie Calculator will be far more relevant than surface area.

A short history of body surface area

The idea of relating drug doses and metabolism to surface area rather than weight goes back to the 19th century, but it was the 1916 paper by Delafield Du Bois and Eugene Du Bois that gave clinicians a usable equation. Working with only nine subjects, they coated bodies in molds to measure surface area directly and then fitted a formula to height and weight. Remarkably, that century-old equation is still in daily clinical use.

Later researchers refined the approach with larger samples and simpler math - Gehan and George (1970) with 401 measurements, Haycock (1978) for children, and Mosteller (1987) with a square-root shortcut that fit on the back of an envelope. The persistence of all four shows how durable the underlying relationship between body size and surface area really is, and why an estimate from height and weight remains trustworthy to within a few percent more than a hundred years on.

Tips for an accurate BSA estimate

• Use recent, measured numbers. A fresh scale weight and a properly measured height beat rounded guesses; even a few pounds or an inch shifts the result.
• Double-check the unit toggle. The single most common error is entering pounds or inches with the metric toggle on (or vice versa). If the result looks impossible, this is almost always why.
• Treat the average as your headline number. When the four formulas agree, their mean is a robust single figure to quote.
• For children, lean on Haycock. It was validated for pediatric bodies, but any actual pediatric decision belongs to a clinician.
• Don't over-interpret tiny differences. A 0.01-0.03 m² gap between formulas is normal rounding, not a meaningful disagreement.

Limitations and assumptions

BSA formulas are convenient but not exact. Keep these limits in mind:

• They were derived from small validation samples (Du Bois used just nine people) and assume an average body shape.
• They use only height and weight, so they ignore body composition, fluid status, edema, and amputations.
• Accuracy drops at the extremes - very small infants and very high body weights fall outside the original validation range.
• Different formulas use different exponents, so a small spread between them is expected, not an error.
• The output is an estimate for standardizing measurements, never a substitute for a clinician's dosing decision.

How it compares to related calculators

This page answers "how large is my body surface area, in m²?" If your real question is different, a sister tool will fit better:

• To check whether your weight is healthy for your height, use the BMI Calculator.
• To find a target weight for your height and frame, use the Ideal Weight Calculator.
• To separate fat from lean mass, use the Body Fat Calculator or the Lean Body Mass Calculator.
• To plan energy needs, use the BMR Calculator for resting metabolism or the Calorie Calculator for daily intake.

Sources

• National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) - kidney disease and GFR reference information.
• National Cancer Institute (NCI), National Institutes of Health - cancer treatment and chemotherapy dosing overview.
• National Library of Medicine (NLM / PubMed) - primary BSA formula publications (Du Bois 1916, Mosteller 1987, Haycock 1978, Gehan-George 1970).