What is body surface area?

The body surface area is the total area of the external surface of a human body and is measured in square meters. As it is difficult to measure directly, it is estimated from height and weight using known formulas.

What is the most accurate formula for calculating body surface area?

There is no one formula that works for everyone. The Du Bois formula is the most commonly used and well validated. The Mosteller formula is popular because of its simplicity, while Haycock and Boyd were developed specifically for children. In most adults all formulas give very similar results.

Why are drugs dosed by body surface area and not weight?

Body surface area is more closely correlated with metabolism than weight, so dosing based on body surface area tends to result in more consistent therapeutic outcomes. For this reason, chemotherapy drugs are usually administered in milligrams per square meter.

How big is a normal body surface?

The rough average for adult males is about 1.9m2 while it's around 1.6m2 for adult females. In children, the values are much lower ranging from about 0.25m2 in newborns to about 1.1m2 at ten years of age.

Does body surface area change by gender?

Only the Schlich formula takes this into account and uses separate equations for men and women. The other seven formulas use only height and weight so that the result is not dependent on gender.

How to calculate body surface area manually?

The simplest method is the Mosteller formula. You multiply your height (in centimeters) by your weight (in kilograms), then divide that result by 3600 before taking the square root. So, for example, if you are 175 cm tall and weigh 70 kg, your result would be about 1.84 m2.

Body Surface Area Calculator

Your measurements

Sex

Dropdown list for MaleFemale

Height

Weight

Formula for the headline result

Every formula estimates the same body surface area a little differently. Du Bois is the clinical default; Mosteller is the easiest to do by hand; Schlich is the only one that uses sex.

Estimate a BSA-based dose

Turn a dose per square metre into a total dose for this body surface area.

Body surface area (m²)

m²

Enter your height and weight to estimate your body surface area and compare all eight formulas.

Please input values into the fields

Compare the formulas

The body surface area (BSA) is the total surface area of the external body and is measured in square meters.

As it cannot be measured simply with a tape measure, it is usually estimated using height and weight. Over the past hundred years researchers have developed various formulas. Although results may vary slightly, comparisons are meaningful.

This calculator will calculate eight of the most popular formulas at once. It displays the estimated value for your selected formula as the main result and lists all results so you can see how they vary from each other.

Here's how to use this calculator.

Enter your height and weight, then select the units you want to use - feet and inches, centimeters, pounds or kilograms.

Select the formula whose estimated value you want to display as your main result. The Du Bois formula is selected by default because it's most commonly used in hospitals.

If you are checking the Schlich estimate please ensure that gender is set correctly. This is the only formula in the list which uses gender. If you need to calculate dose by body surface area open the dosage assistant and enter the dose per square meter.

Comparison formulas:

In the following formulas, weight is given in kilograms, height in centimeters and the result is expressed in square meters. The calculator will convert units for you.

Du Bois and Du Bois (1916):

This is the earliest formula and is still most commonly used in clinical practice today. Studies have shown that it estimates body surface area very accurately for both lean and obese patients.

\text{BSA} = 0.007184 \times W^{0.425} \times H^{0.725}

Mosteller (1987):

Even if you do the calculations in your head or use simple calculation tools, this is the easiest formula and therefore many doctors learn it by heart. If you look at the following formula, you will understand why.

\text{BSA} = \sqrt{\dfrac{W \times H}{3600}}

Haycock (1978)

This formula was developed and validated for infants, children and adults and is therefore often used in pediatrics.

\text{BSA} = 0.024265 \times W^{0.5378} \times H^{0.3964}

Gehan and George (1970)

This formula is based on a large amount of direct measurement data and is often used in cancer research.

\text{BSA} = 0.0235 \times W^{0.51456} \times H^{0.42246}

Boyd (1935)

This is a relatively early formula that works for very small to very large body sizes because the index itself depends on body weight.

\text{BSA} = 0.0333 \times W^{(0.6157 - 0.0188\,\log_{10} W)} \times H^{0.3}

Fujimoto (1968) and Takahira (1968)

These equations were developed based on measurements of Japanese adults and represent a regional alternative to Western equations.

\text{BSA}_{\text{Fujimoto}} = 0.008883 \times W^{0.444} \times H^{0.663}

\text{BSA}_{\text{Takahira}} = 0.007241 \times W^{0.425} \times H^{0.725}

Schlich (2010)

This is the latest formula which is based on a 3D body analysis and it's unique in that it uses separate equations for men and women.

\text{BSA}_{\text{men}} = 0.000579479 \times W^{0.38} \times H^{1.24}

\text{BSA}_{\text{women}} = 0.000975482 \times W^{0.46} \times H^{1.08}

Average body surface area.

The body surface area (BSA) changes as the body grows and is less than one square meter at birth while large adults can have a BSA of about two square meters. The following rough averages will help you get an idea of the magnitude.

Person	BSA (m²)	BSA (ft²)
Newborn child	0.25	2.69
Two-year-old child	0.5	5.38
Ten-year-old child	1.14	12.27
Average adult woman	1.6	17.22
Average adult man	1.9	20.45

A calculator will convert your estimated values into percentages compared to the average adult value. For men this is 1.9m2 and for women it's 1.6m2 so you can see where your values are.

Why body surface area is important in medicine.

The reason why the BSA is used much more often than just weight alone is simple: it's closer to the body's metabolism and therefore reflects physiological state more accurately.

The most common application is for calculating medication dosages. Particularly with chemotherapy, the dosages are almost always given in milligrams per square meter. Adjusting the dose to body surface area leads to more consistent results than adjusting it to weight. If you open the dosage calculator above, you can see how the calculation works when a dose is given in milligrams per square meter.

BSA is also used to standardize cardiac measurements. Dividing the cardiac output by BSA gives the Cardiac Index, which allows doctors to compare heart function in people of different sizes. Kidney function is also reported this way and corrected for a standardized body surface area of 1.73 m2.

This method also has its limitations. When size and weight are extreme, the accuracy of the BSA formula decreases. For drugs with a small margin between effective dose and toxic dose, body surface area alone may not be enough to ensure sufficient accuracy. Still, it is a more stable option for most patients.

What formula should you use?

In typical adults the choice of formula has little effect. The results from these formulas usually differ by only a few percent as shown in the comparison.

If you need a quick solution, use the DuBois formula as it is used by default in most tools and textbooks. If you want to do the math yourself, the Mosteller formula is easiest to remember.

For children the Haycock and Boyd formulas have been validated for a wide age range. If you need a modern estimate that takes into account differences between male and female bodies then use the Schlich formula.

Example calculation

Let's take an example: An adult person with a weight of 70 kg and a height of 175 cm. These values are entered into the Du Bois formula.

\text{BSA} = 0.007184 \times 70^{0.425} \times 175^{0.725} \approx 1.85\ \text{m}^2

According to Mosteller's formula, the body surface area is 1.84 square meters; according to Takahira's formula, it is 1.86 square meters; and according to Fujimoto's formula, it is 1.80 square meters. All of these values are approximately 1.85 square meters, which is a typical value for the body surface area of an average adult and close to the average male value of 1.9 square meters.

This calculator is for general educational purposes only and does not constitute medical advice. The estimated body surface area values are approximations only, and should not be used alone to determine actual medication dosages. You must strictly follow the instructions of a qualified physician and your facility's procedures in all clinical decisions.

Frequently asked questions

What is body surface area?: The body surface area is the total area of the external surface of a human body and is measured in square meters. As it is difficult to measure directly, it is estimated from height and weight using known formulas.
What is the most accurate formula for calculating body surface area?: There is no one formula that works for everyone. The Du Bois formula is the most commonly used and well validated. The Mosteller formula is popular because of its simplicity, while Haycock and Boyd were developed specifically for children. In most adults all formulas give very similar results.
Why are drugs dosed by body surface area and not weight?: Body surface area is more closely correlated with metabolism than weight, so dosing based on body surface area tends to result in more consistent therapeutic outcomes. For this reason, chemotherapy drugs are usually administered in milligrams per square meter.
How big is a normal body surface?: The rough average for adult males is about 1.9m2 while it's around 1.6m2 for adult females. In children, the values are much lower ranging from about 0.25m2 in newborns to about 1.1m2 at ten years of age.
Does body surface area change by gender?: Only the Schlich formula takes this into account and uses separate equations for men and women. The other seven formulas use only height and weight so that the result is not dependent on gender.
How to calculate body surface area manually?: The simplest method is the Mosteller formula. You multiply your height (in centimeters) by your weight (in kilograms), then divide that result by 3600 before taking the square root. So, for example, if you are 175 cm tall and weigh 70 kg, your result would be about 1.84 m2.

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Disclaimer: This calculator is provided for general informational and educational purposes only. Our calculators are under active development, and results may be inaccurate, incomplete, or unsuitable for your situation. Always verify the figures independently and seek advice from a qualified professional before relying on them. We make no warranties and accept no liability for any loss or decision arising from use of this tool.

References

Du Bois D, Du Bois EF (1916): A formula to estimate the approximate surface area if height and weight be known
The original Du Bois body surface area formula.
Mosteller RD (1987): Simplified calculation of body-surface area
The Mosteller square-root formula.
Body surface area — overview and formulas
Background on BSA and the published estimating formulas.