BSA Calculator: Calculate Body Surface Area & Compare Formulas

A Body Surface Area Calculator (BSA Calculator) estimates body surface area from height and weight and reports the result in square meters (m²). This page lets you calculate BSA using the Mosteller formula, compare the result with other established BSA equations, and work with BSA in different units and reference values.

Use the BSA Formula Comparison Calculator to compare Mosteller, Du Bois & Du Bois, Haycock, Gehan & George, and Boyd results for the same height and weight. You can also use the BSA Unit & Reference Calculator to convert BSA between square meters, square feet, and square inches and compare an individual BSA with the commonly used 1.73 m² reference value.

What Is Body Surface Area?

Body surface area (BSA) is an estimate of the total external surface area of the human body. It is normally expressed in square meters (m²).

Unlike body mass index (BMI), which relates weight to height, BSA is an area estimate used in several physiological and clinical calculations. Because directly measuring the complete external surface of the human body is impractical in routine settings, BSA is commonly estimated from measurements such as height and weight.

There is no single BSA equation that produces exactly the same result in every situation. Several formulas have been developed using different populations, measurements, and mathematical approaches. As a result, two established BSA formulas can produce slightly different estimates for the same person.

For general calculations, the Mosteller formula is particularly convenient because it uses a simple square-root equation based on height and weight.

How Is BSA Calculated?

Most commonly used BSA equations require:

• Height
• Weight

The standard inputs for the formulas used on this page are:

• Height in centimeters (cm)
• Weight in kilograms (kg)

If you enter U.S. customary measurements, such as feet, inches, and pounds, the calculator converts them to centimeters and kilograms before applying the selected equation.

Mosteller BSA Formula

The Mosteller formula is:

\(BSA=\sqrt{\frac{H\times W}{3600}}\)

where:

• \(BSA\) = body surface area in m²
• \(H\) = height in centimeters
• \(W\) = weight in kilograms

The Mosteller equation is widely used because it is straightforward to calculate and does not require fractional exponents.

Mosteller BSA Example

Suppose a person is 175 cm tall and weighs 72 kg.

First multiply height by weight:

\(175\times72=12,600\)

Then divide by 3,600:

\(\frac{12,600}{3600}=3.5\)

Finally, take the square root:

\(\sqrt{3.5}\approx1.871\)

Therefore:

\(BSA\approx1.87\text{ m}^2\)

The estimated body surface area is approximately 1.87 m².

BSA Formulas Compared

Mosteller is only one of several established equations for estimating body surface area. The five formulas included in our comparison calculator are:

1. Mosteller
2. Du Bois & Du Bois
3. Haycock
4. Gehan & George
5. Boyd

These formulas use different mathematical relationships between height, weight, and estimated surface area.

Mosteller Formula

\(BSA=\sqrt{\frac{H\times W}{3600}}\)

The Mosteller equation is particularly easy to calculate because it uses only multiplication, division, and a square root.

It is therefore convenient for general-purpose calculations and educational use.

Du Bois & Du Bois Formula

The Du Bois & Du Bois equation is:

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

where height is measured in centimeters and weight in kilograms.

The equation dates to the early development of mathematical BSA estimation and remains one of the commonly referenced formulas.

Haycock Formula

The Haycock equation is:

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

where:

• \(H\) = height in cm
• \(W\) = weight in kg

Haycock is frequently included in comparisons involving children as well as adults. However, the presence of a formula in a general-purpose calculator does not mean it should automatically replace a formula specified by a particular pediatric protocol.

Gehan & George Formula

The Gehan & George equation is:

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

where height is in centimeters and weight is in kilograms.

It is another established empirical BSA equation used in comparisons of BSA estimation methods.

Boyd Formula

The Boyd equation has a more complicated mathematical structure than Mosteller:

\(BSA=0.0003207\times H^{0.3}\times W_g^{(0.7285-0.0188\log_{10}(W_g))}\)

where:

• \(H\) = height in cm
• \(W_g\) = weight in grams

When weight is entered in kilograms, it must be converted to grams for this form of the Boyd equation:

\(W_g=1000\times W\)

The additional logarithmic and exponent terms make Boyd substantially less convenient to calculate manually, but it can be implemented directly in a calculator.

BSA Formula Reference Table

Formula	Height	Weight	Main calculation
Mosteller	cm	kg	Square-root equation
Du Bois & Du Bois	cm	kg	Power equation
Haycock	cm	kg	Power equation
Gehan & George	cm	kg	Power equation
Boyd	cm	kg	Power and logarithmic equation

Other BSA equations also exist, including historical and population-specific formulas. The five above provide a useful comparison set without assuming that every available BSA equation is appropriate for every clinical application.

Compare BSA Formulas

Different formulas can give slightly different BSA values for the same height and weight.

For example, entering the same measurements into Mosteller, Du Bois, Haycock, Gehan & George, and Boyd may produce results that differ by a small amount.

That difference does not automatically indicate that one calculator is wrong. Each equation represents a different mathematical model for estimating BSA.

The comparison calculator shows the BSA produced by each formula using the same height and weight. It can also summarize the lowest result, highest result, average, and spread between the estimates.

Why Do BSA Formulas Give Different Results?

BSA equations were developed from different datasets and using different measurement and modeling approaches.

Consequently, the equations do not describe the relationship between height, weight, and body surface area in exactly the same way. Research comparing BSA equations has shown that the differences can become more noticeable for some body sizes and populations.

Differences may be particularly relevant when considering:

• children
• unusually small body size
• unusually large body size
• obesity
• very tall or very short individuals
• specific clinical populations
• situations where a protocol requires a particular equation

For this reason, it is useful to identify the formula used, rather than reporting a BSA number without any context.

Which BSA Formula Should You Use?

There is no single formula that should automatically be used for every purpose.

For a general-purpose calculation, Mosteller is a practical choice because it is simple, transparent, and widely recognized.

However, if a clinical, research, institutional, or treatment protocol specifies a particular BSA equation, that specified method should be followed.

This distinction is important because formula selection can affect the resulting BSA, and therefore can affect any downstream calculation that uses BSA.

For General Calculations

Mosteller is a convenient general-purpose option.

For Research

Use the equation specified by the study methodology so that results remain consistent with the research protocol.

For Clinical Treatment

Follow the equation and calculation method specified by the relevant healthcare professional, treatment protocol, or guideline.

For Pediatric Applications

Do not assume that one general-purpose BSA equation is automatically appropriate for every child or pediatric application. Pediatric studies have evaluated several different BSA equations, and the appropriate method depends on the intended use.

How to Use the BSA Calculator

Step 1: Choose the Unit System

Select either:

• Metric
• U.S. / Imperial

Step 2: Enter Height

For metric calculations, enter height in centimeters.

For U.S. measurements, enter height in feet and inches.

Step 3: Enter Weight

For metric calculations, enter weight in kilograms.

For U.S. measurements, enter weight in pounds.

Step 4: Select a BSA Formula

The calculator uses Mosteller as the primary formula by default.

You can select another available formula when you specifically need to calculate BSA using that method.

Step 5: Calculate BSA

Select Calculate BSA to obtain the estimated body surface area.

The calculator converts U.S. measurements to the units required by the equations before performing the calculation.

Step 6: Review the Result

The primary BSA result is reported in:

\(\text{m}^2\)

If formula comparison is enabled, you can also review the results produced by the other equations.

BSA Calculation Example Using Metric Units

Consider a person who is:

Height: 180 cm
Weight: 80 kg

Using Mosteller:

\(BSA=\sqrt{\frac{180\times80}{3600}}\)

\(BSA=\sqrt{4}\)

Therefore:

\(BSA=2.00\text{ m}^2\)

The estimated BSA is 2.00 m².

BSA Calculation Example Using U.S. Units

Suppose a person is:

Height: 5 ft 10 in
Weight: 176 lb

First convert the height to inches:

\(5\text{ ft}\times12+10\text{ in}=70\text{ in}\)

Using 2.54 cm per inch:

\(70\times2.54=177.8\text{ cm}\)

Convert the weight to kilograms:

\(176\times0.45359237\approx79.83\text{ kg}\)

Now apply the Mosteller equation:

\(BSA=\sqrt{\frac{177.8\times79.83}{3600}}\)

This gives approximately:

\(BSA\approx1.98\text{ m}^2\)

The calculator performs these conversions automatically when U.S. / Imperial measurements are selected.

BSA Units and Conversions

The standard unit for BSA in medical and physiological applications is square meters (m²).

For general reference, BSA can also be expressed in square feet or square inches.

Convert BSA from Square Meters to Square Feet

The conversion is:

\(1\text{ m}^2=10.7639\text{ ft}^2\)

Therefore:

\(BSA_{\text{ft}^2}=BSA_{\text{m}^2}\times10.7639\)

For example, a BSA of 1.80 m² corresponds to approximately:

\(1.80\times10.7639\approx19.38\text{ ft}^2\)

Convert BSA from Square Meters to Square Inches

Since:

\(1\text{ ft}^2=144\text{ in}^2\)

the conversion can be written as:

\(1\text{ m}^2\approx1550.003\text{ in}^2\)

Therefore:

\(BSA_{\text{in}^2}=BSA_{\text{m}^2}\times1550.003\)

These conversions are useful for understanding the physical area represented by a BSA value, but m² remains the standard unit used in most clinical BSA calculations.

What Does 1.73 m² Mean in BSA?

You may frequently encounter 1.73 m² when reading about BSA and clinical measurements.

It is commonly used as a reference body surface area for indexing certain measurements. It should not be interpreted as a universal BSA that every adult should have.

An individual’s calculated BSA may be higher or lower depending on height, weight, and the equation used.

For example, if a person’s estimated BSA is 1.90 m², that does not mean their BSA is abnormal simply because it differs from 1.73 m².

The purpose of the 1.73 m² reference is to provide a standardized basis for certain indexed measurements.

BSA Relative to 1.73 m²

A simple comparison can be expressed as:

\(\text{BSA Ratio}=\frac{\text{Individual BSA}}{1.73}\)

The percentage relative to the reference is:

\(\text{Percentage of Reference}=\frac{\text{Individual BSA}}{1.73}\times100\)

For example, if BSA is 1.90 m²:

\(\frac{1.90}{1.73}\times100\approx109.8%\)

This means the calculated BSA is approximately 109.8% of the 1.73 m² reference value. It does not by itself indicate whether the person’s BSA is healthy or unhealthy.

What Is an Average or Normal BSA?

There is no single BSA value that is normal for every adult.

BSA varies with body size and therefore naturally differs between individuals.

Height and weight are important determinants of the calculated value, while body proportions and the selected equation can also affect the estimate.

The commonly encountered 1.73 m² value should therefore be understood as a conventional reference used for particular indexing purposes, not as a universal target BSA.

A BSA value by itself also does not determine whether a person is healthy, overweight, underweight, or affected by a particular disease.

BSA for Children

BSA estimation is also used in pediatric settings, but children should not simply be treated as small adults when selecting a formula for a specific clinical application.

Several BSA equations have been evaluated in children, including Haycock, Gehan & George, Mosteller, and other pediatric-specific approaches. Studies comparing pediatric equations demonstrate that the choice of formula can affect the estimated BSA.

Haycock and Pediatric BSA

The Haycock equation is frequently encountered in pediatric BSA discussions because its development included infants, children, and adults.

However, this does not mean Haycock should automatically be substituted for another equation in every pediatric situation.

If a pediatric clinical protocol specifies a particular formula, use that specified formula.

Pediatric BSA and Clinical Decisions

BSA can be used as part of clinical calculations in children, including calculations expressed per square meter.

Because treatment decisions can depend on many factors beyond BSA, an online calculator should not be used independently to determine or change a child’s medication or treatment.

BSA vs Total Body Surface Area in Burn Assessment

The terms body surface area and total body surface area (TBSA) can sometimes cause confusion.

Body Surface Area

BSA generally refers to the estimated total external surface area of the body.

TBSA in Burn Assessment

In burn medicine, TBSA is commonly used to describe the percentage of the body’s surface affected by burns.

For example, a statement such as:

20% TBSA burn

does not mean that the person’s total body surface area is 20%.

It means that an estimated 20% of the person’s body surface is affected by burns.

Burn assessment can use specialized methods such as the Rule of Nines or the Lund-Browder chart. These are different from a general height-and-weight BSA calculator.

Where Is BSA Used?

BSA is used in several medical, physiological, and research contexts.

BSA and Medication Dosing

Some medications are prescribed using dose units expressed per square meter, such as:

\(\text{mg/m}^2\)

In those situations, BSA may form part of the calculation used to determine a dose.

However, the appropriate medication dose cannot be determined from BSA alone. The relevant drug, indication, treatment protocol, patient characteristics, dose limits, organ function, previous treatment, and other factors may also matter.

For this reason, this BSA calculator should not be used to independently determine, change, or verify a medication dose.

BSA and Chemotherapy

BSA has historically been used in some oncology protocols where treatment is expressed in units such as mg/m².

The general mathematical relationship is:

\(\text{Dose}=\text{Dose Density}\times BSA\)

However, this equation describes only the mathematical relationship between a prescribed dose density and BSA. It does not determine what dose density should be used for a particular patient.

Any actual treatment dose should come from the applicable medical protocol and healthcare professional.

BSA and Cardiac Index

BSA can also be used to normalize cardiac output for body size.

The basic relationship is:

\(\text{Cardiac Index}=\frac{\text{Cardiac Output}}{BSA}\)

This allows cardiac output to be expressed relative to estimated body surface area.

BSA and Kidney Function

BSA also appears in the reporting and interpretation of certain kidney-function measurements.

A commonly used reference body surface area is:

\(1.73\text{ m}^2\)

This provides a standardized reference for indexing certain measurements. The distinction between a measurement normalized to 1.73 m² and an individual’s actual BSA can be important in clinical interpretation.

A general BSA calculator should not be used by itself to change medication or treatment based on kidney-function results.

Why Is BSA Expressed in Square Meters?

BSA represents an area, so it is expressed using a square unit.

The standard clinical unit is:

\(\text{m}^2\)

For example:

\(1.80\text{ m}^2\)

means an estimated body surface area of approximately 1.80 square meters according to the selected equation.

Square feet and square inches can be useful for unit conversion, but m² is the standard unit for most medical applications.

Can BSA Be Measured Directly?

Body surface area can theoretically be measured using more direct techniques, including methods based on physical measurement or three-dimensional body imaging.

Such approaches are much more complicated than calculating BSA from height and weight and are not practical for routine calculator use.

Height-and-weight equations therefore provide a convenient way to estimate BSA without directly measuring the body’s entire external surface. Research comparing BSA equations with more detailed measurement approaches also demonstrates that these equations are estimates rather than perfect representations of individual anatomy.

How Accurate Is a BSA Calculator?

A BSA calculator can accurately perform the mathematical calculation associated with a selected equation, but that does not mean the result is an exact measurement of the person’s physical surface area.

There are two different issues:

Calculation accuracy: whether the calculator correctly applies the selected formula.

Estimation accuracy: how closely that formula represents the individual’s actual body surface area.

The second issue depends on the equation, population, body size, measurements, and other factors.

Different published BSA equations can therefore produce different estimates for the same person.

Limitations of BSA Calculations

Important limitations include:

• BSA is an estimate rather than a direct measurement.
• Different equations can produce different results.
• Incorrect height or weight measurements affect the calculation.
• Body proportions are not fully captured by height and weight alone.
• Some populations may not be represented equally by the original datasets used to develop particular formulas.
• Pediatric and unusual body-size applications may require a specific formula or protocol.
• BSA alone does not diagnose a medical condition.

BSA Calculation Examples

Example 1: 175 cm and 72 kg

Using Mosteller:

\(BSA=\sqrt{\frac{175\times72}{3600}}\)

\(BSA=\sqrt{3.5}\approx1.87\text{ m}^2\)

Example 2: 180 cm and 80 kg

\(BSA=\sqrt{\frac{180\times80}{3600}}\)

\(BSA=\sqrt{4}=2.00\text{ m}^2\)

Example 3: 5 ft 10 in and 176 lb

Convert:

\(70\text{ in}\times2.54=177.8\text{ cm}\)

\(176\text{ lb}\times0.45359237\approx79.83\text{ kg}\)

Then:

\(BSA=\sqrt{\frac{177.8\times79.83}{3600}}\approx1.98\text{ m}^2\)

These examples demonstrate why the calculator can accept either metric or U.S. measurements while applying the BSA equations using the required metric units.

History of BSA Formulas

Several important BSA equations have been developed over more than a century.

Du Bois & Du Bois

The Du Bois & Du Bois equation was published in 1916 and became an important historical BSA estimation method. (PubMed Central (PMC))

Boyd

The Boyd equation was published in 1935 and uses a more complicated relationship involving height, weight, and a logarithmic term.

Gehan & George

The Gehan & George equation was developed in the 1970s as another empirical method for estimating BSA from height and weight.

Haycock

The Haycock equation was published in 1978 and is among the formulas frequently evaluated in pediatric BSA research.

Mosteller

Mosteller published the simplified BSA equation in 1987, providing a much easier calculation than several earlier equations.

The continued use of several formulas reflects the fact that BSA is estimated from body measurements rather than directly determined by a single universally accepted equation.

Frequently Asked Questions

What is BSA?

BSA stands for body surface area. It is an estimate of the total external surface area of the body and is usually expressed in square meters (m²).

How do I calculate BSA?

One commonly used method is the Mosteller formula:

\(BSA=\sqrt{\frac{Height(cm)\times Weight(kg)}{3600}}\)

Other established formulas can produce slightly different estimates.

What is the Mosteller BSA formula?

The Mosteller formula is:

\(BSA=\sqrt{\frac{H\times W}{3600}}\)

where height is measured in centimeters and weight in kilograms.

Which BSA formula should I use?

For general calculations, Mosteller is a convenient option. If a clinical, research, or institutional protocol specifies a particular equation, use that specified equation instead.

Why do BSA calculators give different answers?

Different BSA equations were developed using different data, measurement approaches, and mathematical models. Therefore, they can produce slightly different estimates for the same height and weight.

What is a normal BSA?

There is no single BSA value that is normal for every adult. BSA varies according to body size and other characteristics.

What does 1.73 m² mean in BSA?

1.73 m² is a conventional reference body surface area used when certain measurements are indexed to a standardized body size. It is not a universal target or required BSA for every person.

Is BSA the same as BMI?

No. BSA estimates body surface area, while BMI is a weight-for-height index. They use height and weight differently and serve different purposes.

Can I calculate BSA using feet and pounds?

Yes. The calculator can convert feet/inches and pounds into centimeters and kilograms before applying the selected BSA formula.

Can BSA be converted to square feet?

Yes.

\(BSA_{\text{ft}^2}=BSA_{\text{m}^2}\times10.7639\)

Can BSA be converted to square inches?

Yes.

\(BSA_{\text{in}^2}=BSA_{\text{m}^2}\times1550.003\)

What BSA formula is used for children?

Several equations have been studied in children, including Haycock, Gehan & George, and Mosteller. The appropriate equation depends on the specific clinical or research application, so a pediatric protocol should be followed when one is specified.

Is BSA used for medication dosing?

Yes, some treatment protocols express doses in units such as mg/m². However, BSA is only one part of such calculations, and a general calculator should not be used independently to determine or change a medication dose.

Is BSA the same as the percentage of body surface burned?

No. BSA is an estimate of total body surface area. A burn measurement such as 20% TBSA refers to the percentage of body surface affected by burns.

Can BSA be calculated from height alone?

Not with the commonly used height-and-weight BSA equations. These equations require both height and weight.

Can BSA be calculated from weight alone?

Not with the standard formulas used on this page. Height is also required.

What unit is BSA measured in?

The standard unit is square meters (m²).

How accurate is a BSA calculator?

A calculator can correctly apply the selected equation, but the resulting BSA remains an estimate. Different equations can produce different estimates for the same person.

Key Takeaways

• BSA stands for body surface area and is normally expressed in m².
• The commonly used BSA equations require height and weight.
• Mosteller provides a simple general-purpose BSA calculation.
• Other established formulas include Du Bois & Du Bois, Haycock, Gehan & George, and Boyd.
• Different BSA formulas can produce slightly different results.
• The BSA Formula Comparison Calculator lets you compare these equations using the same measurements.
• BSA can be calculated from either metric or U.S./Imperial measurements.
• BSA can be converted between m², ft², and in².
• 1.73 m² is a conventional reference value used for certain indexing applications; it is not a universal normal BSA.
• BSA and BMI are different measurements and should not be used interchangeably.
• Pediatric applications may require a particular BSA equation or clinical protocol.
• BSA can appear in medication-dosing, cardiac-index, renal-function, and other clinical contexts.
• A general BSA calculator should not be used by itself to make medication or treatment decisions.
• When a clinical or research protocol specifies a particular BSA formula, that specified method should take precedence.

Medical note: This calculator provides an estimated body surface area from height and weight. It is intended for informational and educational use and should not be used by itself to diagnose a condition, determine a medication dose, or change treatment. When BSA is required for clinical care, follow the equation and protocol specified by the appropriate healthcare professional or guideline.