Body Surface Area Calculator

Body Surface Area Calculator: BSA in m², Every Major Formula

Use this body surface area calculator to calculate BSA in square meters using multiple approved algorithms at once. Body surface area is a clinical measurement used to index parameters like cardiac output and to scale a few drug computations. It is not a general fitness number. Most of the sites that include calculators implement a single formula without even mentioning it most of the time and never say that there are other approved formulae that provide somewhat different responses. This body surface area calculator allows you to put a number of formulas side by side on the same measurements so you can examine how much they agree and where they don’t. This page has ONLY the BSA figure. It does not compute drug doses, and any dosing choice must be made by a competent prescriber according to institutional practice.

What Body Surface Area Is Used For

Body surface area is an estimate of the entire surface area of a human body. It is represented in square meters (m²) and is based on height and weight. This is because surface area is more directly related to metabolic rate and physiological function than weight alone and is therefore effective for normalizing some metrics to an individual’s actual body size rather than simply to weight.

In clinical practice, BSA is encountered in several recurring contexts: in the indexing of cardiac output to give a cardiac index that is comparable across patients of different sizes, in the scaling of some medication calculations (most notably in oncology and pediatrics), in the assessment of the extent of burns in terms of a percentage of total body surface area, and in the indexing of kidney function measures such as glomerular filtration rate. In either scenario BSA provides a fair means for clinicians to compare or scale a measurement across patients of widely diverse sizes.

This page calculates BSA only with the help of a body surface area calculator. This is the border that counts most on this site, expressed openly and upfront, not hidden away in a footer. It is a reference and teaching tool. It is not a validated clinical program and does not compute any kind of medicine doses. Any dose or clinical choice must be made by a qualified prescriber using their institution’s unique protocols, not 

The Measurements We’ll Use

We’ll take one set of measurements and run them through every formula on this body surface area calculator, so the results are comparable: a person who is 175 cm tall and weighs 70 kg.

The BSA Formulas Compared

There are a number of formulas in approved clinical use, and they do not all provide exactly the same result. So here’s how to calculate body surface area using a body surface area calculator, on the basis of our example measurements.

Mosteller

BSA (m²) = √(height cm × weight kg / 3600)

Applied: √(175 * 70 / 3600) = √12,250 / 3,600 = √3.403 = 1.84 m²

The Mosteller formula is the most commonly employed in day-to-day clinical practice, primarily because it is simple enough to be calculated by hand or quickly checked at the bedside, unlike the exponent-heavy formulations below.

Du Bois and Du Bois

BSA (m²) = 0.007184 x height (cm) ^ 0.725 x weight (kg) ^ 0.425

0.007184 * 175^0.72 applied to the same measurements5 × 70^0.425 ≈ 1.85 m²

This is the oldest formula in regular use. It was first derived in 1916 and is still often quoted as a reference standard despite having been developed from a small sample.

Haycock

BSA (m²) = 0.024265 × height (cm)0.3964 × weight (kg)0.5378

Applied: 0.024265* 175^0.3964 * 70^0.5378 = 1.85 m^2

Partly because Haycock was designed with pediatric populations in mind, it is regularly found in children’s dosage procedures and the medical literature.

Gehan and George

BSA (m²) = 0.0235 x height (cm) ^ 0.42246 x weight (kg) ^ 0.51456

Applied: 0.0235 * 175^0.42246 * 70^0.51456 = ~1.85 m²

Gehan-George was developed from a broader and more diversified sample than Du Bois and is still cited in some cancer applications.

Why the Formulas Disagree, and When It Matters

Here are all four results on the identical 175 cm, 70 kg patient:

At this rather standard adult size, the variation between formulas is modest, hardly 0.01 m².  This is no mere coincidence of good formula agreement; it is because these formulas were each derived from real measured populations, using different methods and different groups of people. Some divergence is to be expected, and it tends to show up more clearly at the extremes of body size, rather than in the middle of the range. 

To show it well, let us see the same four calculations calculated on a body surface area calculator applied to a young toddler of 90 cm and weighing 12 kg. 

The absolute spread here is only 0.02 m², but proportionally that’s a far greater gap compared to the whole value than the adult instance before, about 3.6% of the whole vs. roughly 0.5% for the adult case. This is precisely the pattern described in the clinical literature: formula choice is more important at the extremities of body size, where precision often counts most. 

The practical point for physicians and students is not what formula is objectively “best.” It is knowing what formula a particular protocol or study or institutional source provides, and applying that one formula consistently, rather than thinking that any BSA value is interchangeable with any other. A cardiac index estimated using a Du Bois BSA and a cardiac index calculated using a Mosteller BSA for the same patient are not really the same figure, although both are technically “the body surface area calculator.” When comparing a value to a reference range or to a previous measurement for the same patient, using the same formula both times matters more than which formula was originally chosen. 

BSA in Children

A lot of the time, BSA body surface area formula measurements are done in pediatric settings, more often than in general adult care. Mosteller and Haycock are the two formulas that are used most often in pediatric literature and practices. Haycock was made from measurements of children only; Mosteller is easy to use and good for a wide age range.

For the same reasons as the above comparison, picking the right formula is even more important for small patients, since the differences between formulas are bigger for smaller bodies. A difference that doesn’t seem important to a normal-sized adult might be very important to a baby or small child. This website is only about that pattern. It does not give any dose suggestions for children; that is the job of the qualified prescriber following the institutional protocol.

Units and Common Errors

Before you believe any BSA result, here are some useful things you should know:

The body surface area calculator is always given in m², never in square centimeters or any other measure. Most people make the mistake of entering the wrong unit of height. Usually inches instead of centimeters or the other way around. This is not a small difference; it’s a big one.

Background information: Different adults have different BSA values, but most fall between 1.5 and 2.2 m². It depends on their body size. Those that are very far outside of that range, especially those that are off by 10 or more, almost always show an unusual patient or a mistake in entering the unit, so they should be checked again before being used.

Conclusion

The body surface area calculator is a number, second, a clinical scale, first. The crucial issue is to know what it is used for and what formula a particular source is using, rather than taking any one BSA result as definitive. The formulas agree well for typical adult sizes and diverge significantly at the extremes, which is worth bearing in mind where precision is really needed, particularly in pediatric and cancer situations where the numbers are already small and every proportional variation counts.

FAQs

Q1. How do you calculate body surface area?

The Mosteller formula is used most of the time: BSA (m²) = √((height cm × weight kg) ÷ 3600). That’s about 1.84 m^2 for someone who is 175 cm tall and 70 kg. For average adult measures, results from other well-known formulas, such as those by Du Bois, Haycock, and Gehan-George, are pretty much the same.

Q2. Which BSA formula should I use?

Whichever formula is given by the relevant study, protocol, or institutional source. It’s more important to be consistent with the source you’re using than to choose the theoretically best formula, since formulas aren’t always interchangeable.

Q3. Why do different BSA calculators give different answers?

This is because each equation was generated from a different population and utilized different measurement techniques. Differences are normally minimal for ordinary adult sizes but become proportionally larger at the extremes of physical size, for example, in little children or very large adults.

Q4. What is a normal BSA?

There is no “normal” value, because BSA is scaled to body size rather than a health state. Typical adult values are in the range of about 1.5 to 2.2 m². This is a descriptive range based on normal body sizes, not a health measure.

Q5. Is BSA the same as BMI?

No. BSA is an estimate of total body surface area in square meters. BMI is a ratio of weight to height and used as a screening tool. They’re computed differently and utilized for distinct purposes. BSA is essentially a clinical scaling parameter, whereas BMI is a general weight-screening metric.

Q6. Can I use this to work out a medication dose?

No. This calculator is exclusively for BSA. It does not compute drug doses. It is not a validated clinical dosing software. Medication dose decisions must be determined by a qualified prescriber following their institution’s particular standards and not by a number from this or any general calculator.