Body Surface Area Calculator
Estimate your BSA in m² with the Du Bois & Mosteller formulas
🧍 Your measurements
Last updated June 2026
Method: BSA is computed from height and weight using the peer-reviewed Du Bois & Du Bois (1916) and Mosteller (1987) formulas, plus Haycock (1978) and Gehan-George (1970) for comparison. All inputs are converted to kilograms and centimeters before calculation.
Included: Du Bois, Mosteller, Haycock and Gehan-George results in m², their average, and imperial (lbs, ft/in) or metric (kg, cm) input.
Not included: Drug-specific dosing, capped BSA (some protocols cap at 2.0 m²), body fat, fluid status or amputations - all of which a clinician must account for.
Not medical advice - this is an estimate. Dosing and clinical decisions must be made by a qualified healthcare professional.
Body surface area calculator: how it works
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:
BSA = 0.007184 × weight(kg)0.425 × height(cm)0.725 A simpler and extremely popular alternative is the Mosteller formula, which is easy to compute by hand:
BSA = √( weight(kg) × height(cm) ÷ 3600 ) 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:
- 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.
- 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).
- 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.
- 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 and Ideal Weight calculators are the right tools; BSA answers a separate, dosing- and physiology-focused question.
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.
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).
⚠️ Common mistakes & edge cases
Using BSA to self-dose medication
BSA-based dosing is set by clinicians, who may cap BSA, adjust for organ function, or use a different formula entirely. Never use an online BSA value to decide or change a dose.
Mixing up units
The formulas require kilograms and centimeters. Entering pounds where kilograms are expected (or inches where centimeters are expected) inflates the result dramatically. This tool converts for you - just make sure the correct unit toggle is selected.
Expecting different formulas to match exactly
Du Bois, Mosteller, Haycock and Gehan-George each use slightly different exponents, so small differences (a few percent) are normal and expected - not an error.
Applying adult formulas to infants
Du Bois can underestimate BSA in very small children. Haycock was developed specifically for infants and children; for pediatric use, prefer it - and always defer to a pediatrician.
❓ Frequently asked questions
What is body surface area (BSA)?
Body surface area is the total measured surface of the human body, expressed in square meters (m²). Because it scales with both height and weight, clinicians often use BSA instead of body weight alone for things like chemotherapy dosing, cardiac index and burn assessment. An average adult is roughly 1.7 m².
How is BSA calculated?
The most common method is the Du Bois formula: BSA = 0.007184 × weight(kg)^0.425 × height(cm)^0.725. A simpler, very popular alternative is the Mosteller formula: BSA = √(weight(kg) × height(cm) / 3600). This tool computes both, plus the Haycock and Gehan-George formulas, and shows their average.
Which BSA formula is most accurate?
There is no single 'most accurate' formula for every person. Du Bois & Du Bois (1916) is the historic standard and Mosteller (1987) is favored for its simplicity and good agreement. For children, Haycock is often preferred. In practice the formulas usually agree within a few percent, so most clinicians pick one and use it consistently.
What is a normal body surface area?
There is no strict 'normal' value, but typical adults fall in roughly 1.5–2.0 m². The often-cited average is about 1.73 m² for adults (frequently used as a reference, for example in kidney function calculations). Children have much smaller BSA, which is why pediatric dosing relies on it heavily.
Why is BSA used for medication dosing?
Many drugs - especially chemotherapy agents - are dosed per square meter of body surface area because BSA correlates better with metabolic rate, blood volume and organ size than body weight alone. This helps standardize dosing across patients of different sizes. Actual dosing is always determined by a clinician.
Should I use imperial or metric units?
Either works - this calculator converts for you. Enter feet/inches and pounds (the default for US users), or switch to centimeters and kilograms. Internally every formula uses kilograms and centimeters, so the result is identical regardless of which units you enter.
Is this BSA calculator suitable for children?
It will compute a value for any valid height and weight, and includes the Haycock formula often used in pediatrics. However, pediatric dosing and clinical decisions are highly individual - never use an online estimate to determine a child's medication. Always consult a pediatrician or pharmacist.
What is the difference between Du Bois and Mosteller BSA?
Both estimate the same quantity from height and weight, but with different math. Du Bois (1916) uses two separate exponents, 0.425 for weight and 0.725 for height, derived from measurements of just nine subjects. Mosteller (1987) simplifies this to a single square-root formula that is far easier to compute by hand and tends to agree with Du Bois within about 1-2% for most adults. Mosteller is the most widely used in modern oncology because of its simplicity; Du Bois remains the historic reference. The choice rarely changes the result enough to matter clinically.
Does muscle, fat, or body composition affect BSA?
The standard formulas use only height and weight, so they cannot distinguish muscle from fat. Two people with identical height and weight get the same BSA even if one is lean and one is not. This is a known limitation: BSA was designed as a quick proxy for metabolic size, not a body-composition measure. For questions about lean tissue, a Lean Body Mass or Body Fat calculator is more appropriate.
Why do some dosing protocols cap BSA at 2.0 m²?
Very high BSA values would lead to large drug doses, and the relationship between BSA and toxicity is not perfectly linear at the extremes. To reduce the risk of overdosing larger patients, some chemotherapy protocols cap the BSA used for dosing - commonly at 2.0 m² - or use 'dose banding.' Whether a cap applies depends entirely on the specific drug and protocol, which is a clinical decision. This calculator reports the true uncapped BSA.
How accurate is a BSA estimate from height and weight?
For typical adults, BSA formulas are accurate to within a few percent of directly measured surface area, which is why they have been trusted for over a century. Accuracy is lower at the extremes - very small infants, people with very high body weight, amputations, or significant edema can fall outside the range the formulas were validated on. Because of this, BSA is treated as a reliable estimate for standardizing measurements, not as an exact anatomical measurement.
💡 Good to know
1.73 m² is the famous reference value
Kidney function (GFR) is conventionally reported per 1.73 m², the BSA of an "average" adult from mid-20th-century data. That is why you will often see the number 1.73 attached to lab results - it is a normalization, not a target you should aim for.
A unit mix-up is the most common error
The formulas expect kilograms and centimeters. If your result looks wildly off, the usual culprit is entering pounds or inches with the wrong unit toggle selected. The four formulas agreeing closely is a quick sanity check that your inputs are right.
For children, prefer Haycock
Adult-derived formulas can underestimate surface area in infants. Haycock (1978) was developed specifically for children and is shown here for that reason - but any pediatric dosing decision belongs to a pediatrician or pharmacist, never an online estimate.