Body Surface Area (BSA) Calculator
Calculate your Body Surface Area (BSA) using the Du Bois formula—one of the most widely used formulas in clinical practice. BSA is a key metric used in medicine for drug dosing, chemotherapy, and assessing metabolic rate. Get your personalized BSA estimate in seconds.
How to Use This Tool
1. Enter Weight
kg or lbs
2. Enter Height
cm or inches
3. Get Results
View BSA & category
Formula & Calculation
Results in square meters (m²)
Results are rounded to 2 decimal places for clarity.
Quick Reference BSA Table
| Weight (kg) | Height (cm) | BSA (m²) | Category |
|---|---|---|---|
| 50 | 155 | 1.49 | Below Average |
| 60 | 165 | 1.66 | Below Average |
| 70 | 175 | 1.84 | Average |
| 80 | 180 | 1.99 | Average |
| 90 | 185 | 2.13 | Above Average |
| 100 | 190 | 2.27 | Above Average |
How We Calculated
- Input: We collected your weight and height.
- Conversion: Weight is converted to kg, height to cm.
- Formula: Applied the Du Bois formula: BSA = 0.007184 × Weight^0.425 × Height^0.725.
- Category: Compared your BSA to standard ranges to determine the category.
Why Trust This Tool?
Clinically validated standard
No server storage
Use instantly
Works on all devices
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Accuracy & Standards
This calculator uses the Du Bois formula, which is one of the most widely used and validated formulas for estimating Body Surface Area in clinical practice. Results are rounded to 2 decimal places. The tool is for educational purposes—not a substitute for professional medical advice.
Unit Relationship
1 kg = 2.20462 lbs
1 in = 2.54 cm
1 m² = 10.764 ft²
Learn About Body Surface Area
What is BSA?
Body Surface Area (BSA) is a measure of the total surface area of the human body. It's used in medical settings for drug dosing, chemotherapy, and various clinical assessments.
Why BSA Matters
BSA is essential for calculating medication dosages, especially for chemotherapy and other treatments where precise dosing is critical. It's also used in assessing metabolic rate and cardiovascular function.
BSA vs BMI
BMI measures body fat based on weight and height, while BSA measures total body surface area. Both are used in medical contexts, but BSA is more relevant for drug dosing and metabolic assessments.
Real-World Examples
- Example 1: 70 kg, 175 cm → BSA: 1.84 m² (Average)
- Example 2: 60 kg, 165 cm → BSA: 1.66 m² (Below Average)
- Example 3: 90 kg, 185 cm → BSA: 2.13 m² (Above Average)
Limitations of This Tool
- Provides estimates—individual BSA may vary.
- Does not account for age, gender, or body composition differences.
- Not suitable for children or individuals with extreme body proportions.
- Always consult a healthcare professional for clinical decision-making.
Trust & Privacy
We take your privacy seriously. This tool:
- Does not store data on any server
- All calculations happen locally in your browser
- No cookies are used for this tool
References
- Du Bois D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known. Arch Intern Med. 1916.
- Mosteller RD. Simplified calculation of body-surface area. N Engl J Med. 1987.
- National Institutes of Health. Body Surface Area. NIH.gov.
Editorial Process
The Healthtus editorial team, consisting of healthcare professionals and medical writers, reviews this tool regularly to ensure accuracy and alignment with the latest medical standards. We update the content and references as new research emerges.
Last reviewed: July 2026
Frequently Asked Questions
Related Health Tools
Body Surface Area Calculator: Calculate BSA From Height and Weight
A Body Surface Area Calculator estimates the external surface area of the body from measurements such as height and weight. Body surface area, or BSA, is usually expressed in square meters (m²) and is used in several areas of medicine, including indexing certain physiological measurements and calculating doses for some medications.
Several formulas can estimate BSA. The Mosteller formula is particularly popular because it is simple to calculate and uses only height and weight. Other established equations include the Du Bois, Haycock, Gehan-George, and Boyd formulas.
Quick answer: Using the Mosteller formula, BSA is calculated as √[(height in cm × weight in kg) ÷ 3600]. For example, a person who is 170 cm tall and weighs 70 kg has an estimated BSA of about 1.82 m².
What Is a Body Surface Area Calculator?
A Body Surface Area Calculator estimates the body’s external surface area from height and weight.
BSA is not the same as body weight, BMI, or body fat percentage. It is a separate anthropometric measurement that is particularly useful when a physiological measurement or treatment needs to be considered in relation to overall body size.
BSA has been used in clinical calculations such as cardiac index and in some medication-dosing protocols. It is also relevant to kidney-function reporting because eGFR is conventionally normalized to a standard body surface area of 1.73 m².
The calculator does not physically measure your body’s surface area. Instead, it applies a mathematical formula to your measurements.
What Is Body Surface Area (BSA)?
Body Surface Area (BSA) is an estimate of the total external area of the human body.
It is usually reported in:
m²
The concept has been used in medicine for more than a century. The original Du Bois and Du Bois equation was developed in the early 20th century, and numerous alternative equations have since been proposed. More than 40 BSA formulas have appeared in the medical literature over time.
Unlike BMI, which is mainly a weight-for-height screening measure, BSA is intended to represent body size in terms of surface area.
That makes BSA useful for specific clinical calculations, but it should not be interpreted as a general measure of health or fitness.
How Does a BSA Calculator Work?
Most BSA calculators use two basic measurements:
Height
and
Weight
The calculator then applies a BSA equation.
For example, the Mosteller formula uses:
Height in centimeters / inches
Weight in kilograms / pound
and produces:
BSA in m²
The calculation is:
BSA = √[(Height × Weight) ÷ 3600]
Different equations use different mathematical relationships, so two BSA calculators may produce slightly different results from the same height and weight.
That does not necessarily mean that one calculator is broken. It may simply be using a different established equation. Research has found measurable differences between BSA formulas, particularly at some extremes of height and weight.
Body Surface Area Formula
Several BSA equations are used in medicine and research. Healthtus should clearly identify which equation the live calculator uses.
Mosteller Formula
The Mosteller formula is:
BSA (m²) = √[(Height in cm × Weight in kg) ÷ 3600]
The formula was published by R. D. Mosteller in 1987 as a simplified method for calculating body surface area.
Its main advantage is simplicity. You do not need complicated exponents or a nomogram.
Worked Example Using Mosteller
Suppose a person is:
Height: 170 cm
Weight: 70 kg
First multiply height by weight:
170 × 70 = 11,900
Then divide by 3,600:
11,900 ÷ 3,600 = 3.3056
Finally, take the square root:
√3.3056 ≈ 1.82
Therefore:
Estimated BSA = 1.82 m²
The calculator performs these steps automatically.
Du Bois Formula
The classic Du Bois and Du Bois formula is:
BSA = 0.007184 × Height(cm)^0.725 × Weight(kg)^0.425
The original equation dates to 1916 and became one of the most widely referenced BSA formulas.
However, the original derivation was based on a very small sample, and later researchers have questioned how universally appropriate it is.
That is one reason it is useful to describe Du Bois as an established historical formula, rather than automatically calling it the most accurate formula for everyone.
Haycock Formula
The Haycock equation is:
BSA = 0.024265 × Weight(kg)^0.5378 × Height(cm)^0.3964
The Haycock formula was developed from measurements of 81 subjects ranging from premature infants to adults. The researchers reported a very strong fit across a wide range of body surface areas.
This makes the equation particularly relevant when discussing pediatric BSA calculations.
Which Formula Does the Healthtus Calculator Use?
This should be stated clearly on the actual tool page.
For example:
Our Body Surface Area Calculator uses the Mosteller formula to estimate BSA from height and weight.
Only use this statement if the live Healthtus calculator actually uses Mosteller.
This kind of formula transparency is especially important for a medical calculator because different equations can produce different estimates.
Why Is Body Surface Area Used in Medicine?
BSA is not usually calculated just to obtain a general “body size score.” Its importance comes from specific clinical applications.
Medication Dosing
BSA has historically been used for dosing some medications, particularly drugs used in oncology.
Some treatment protocols express medication doses as:
mg/m²
In that situation, BSA is multiplied by the protocol-specific dose per square meter.
However, this does not mean that patients should calculate medication doses themselves.
The correct dose can depend on the medication, treatment protocol, kidney and liver function, age, laboratory values, disease characteristics, previous treatment, dose limits, and many other factors.
Chemotherapy
BSA-based dosing has traditionally been important in chemotherapy.
For example, a protocol might specify a dose in:
mg/m²
But chemotherapy dosing is highly specialized. Different drugs and treatment protocols can use different dosing strategies, and dose modifications may be required for organ function, toxicity, previous treatment, or other clinical factors.
Therefore, a BSA calculator should never be used by itself to calculate or change a chemotherapy dose.
Cardiac Index
BSA is also used when calculating the cardiac index.
The simplified relationship is:
Cardiac Index = Cardiac Output ÷ BSA
Expressing cardiac output relative to BSA helps clinicians account for differences in body size when assessing cardiovascular function. BSA is therefore useful as an indexing measure in clinical physiology.
Kidney Function
BSA has an important relationship with kidney-function measurements.
Standard eGFR values are normally reported as:
mL/min/1.73 m²
The 1.73 m² represents a standardized body-surface area.
This allows eGFR results to be reported in a consistent way across people of different body sizes.
Your GFR Calculator provides an estimate of kidney filtration, while the BSA Calculator estimates body surface area. They are related clinically but are not interchangeable measurements.
Pediatric Medicine
BSA can also be useful in pediatric medicine because children vary considerably in size as they grow.
However, children do not have exactly the same body proportions as adults, so formula selection matters.
The Haycock equation was specifically developed using subjects ranging from premature infants through adults.
For pediatric medication dosing, clinicians should use the appropriate pediatric dosing protocol rather than relying on a general online calculator.
BSA vs BMI: What’s the Difference?
BSA and BMI are sometimes confused because both use height and weight.
They are actually designed for different purposes.
Body Surface Area
BSA:
- Estimates external body surface area
- Is usually expressed in m²
- Is mainly used in medical calculations and physiological indexing
- Is calculated from measurements such as height and weight
Body Mass Index
BMI:
- Relates weight to height
- Is mainly used as a screening measure for weight categories
- Is expressed as kg/m²
- Does not estimate body surface area
The BMI formula is:
BMI = Weight (kg) ÷ Height² (m²)
So BSA should not replace BMI, and BMI should not replace BSA.
They answer different questions.
You can use the BMI Calculator if you want to understand your weight-to-height classification.
What Is a Normal Body Surface Area?
There is no single “normal BSA” that applies to every adult.
BSA changes with body size, particularly height and weight. A child, small adult, and very tall adult can have very different BSA values without that automatically indicating a health problem.
A broad adult BSA range may commonly fall around 1.5 to 2.2 m², but this should be treated only as a rough descriptive range, not a healthy or ideal target.
There is no medically meaningful goal of trying to increase or decrease your BSA.
What matters is how BSA is being used in the specific clinical context.
How Accurate Is a BSA Calculator?
A BSA calculator produces an estimate, not a direct physical measurement.
Several factors explain why estimates can differ.
Different Formulas
Mosteller, Du Bois, Haycock, Gehan-George, Boyd, and other equations can produce different results from the same height and weight.
Research comparing BSA equations has found differences across formulas, including at extremes of body size.
Height and Weight Are Proxies
A formula estimates surface area from height and body mass. It does not directly measure every part of the body.
Body shape and proportions therefore cannot be represented perfectly by a simple height-weight equation.
Extreme Body Sizes
Some formulas may perform differently in people who are particularly short, tall, light, or heavy.
One study comparing Mosteller and Du Bois formulas at extremes of height and weight found differences that could become clinically relevant in some chemotherapy-dosing scenarios.
This is another reason why a medical professional should select and verify the appropriate BSA method when treatment depends on the result.
Body Composition
Height and weight do not directly tell the calculator how much of your weight is muscle, fat, bone, or water.
That means two people with similar height and weight can still have different body shapes and composition.
BSA should therefore not be interpreted as a measurement of body composition.
BSA in m²: What Does the Unit Mean?
BSA is expressed in:
square meters (m²)
For example:
BSA = 1.82 m²
This is an area measurement.
It does not mean:
- 1.82 kg of body weight
- a BMI of 1.82
- 1.82 liters of body volume
The square-meter unit is used because the quantity being estimated is an area.
Body Surface Area and Kidney Function
BSA has a particularly interesting connection to kidney-function testing.
Your eGFR result is commonly reported normalized to:
1.73 m²
This standardization helps make kidney-filtration estimates comparable across different body sizes.
The relationship also explains why BSA sometimes appears in discussions about converting a normalized eGFR to an individual’s absolute GFR for specific clinical purposes.
That calculation should not be used casually, because the appropriate interpretation depends on the clinical situation and the purpose of the measurement.
For more information, see the GFR Calculator.
Body Surface Area for Medication Dosing
BSA can be useful when a medication protocol specifically calls for a dose based on square meters.
But not every medication uses BSA.
Depending on the drug, dosing may instead be based on:
- Fixed dose
- Actual body weight
- Ideal body weight
- Adjusted body weight
- Body surface area
- Kidney function
- Body composition
- Other patient-specific factors
Even when BSA is used, the final prescription is determined by the medication’s clinical protocol and the patient’s medical situation.
Important Medical Note
Do not use this calculator to independently determine a medication or chemotherapy dose. A BSA result is only one input in some clinical dosing protocols, and the appropriate formula and dose must be determined by a qualified healthcare professional.
Common Mistakes and Misconceptions
“BSA and BMI are basically the same thing.”
No. BSA estimates body surface area, while BMI relates weight to height for weight-status screening.
“There is one perfect BSA formula.”
No. Numerous equations exist, and different formulas can produce different results.
“A larger BSA means someone is unhealthy.”
Not necessarily.
BSA primarily reflects body size. It is not a direct score for fitness, health, or body composition.
“BSA tells me how much body fat I have.”
It does not.
BSA does not directly measure body fat percentage or lean body mass.
For body-composition information, see the Body Fat Calculator or Lean Body Mass Calculator.
“I can use BSA to calculate my medication dose.”
Do not do this.
Online BSA calculations are educational estimates. Medication dosing must follow the appropriate prescribing information and clinical protocol.
“My BSA should stay exactly the same.”
No.
Because BSA depends partly on body weight, a substantial change in weight can change the estimated BSA.
Factors That Affect Body Surface Area
The main inputs used by common BSA equations are:
Height
Taller people generally have a larger estimated body surface area.
Weight
Weight is another major input in BSA equations.
Body Proportions
Traditional equations cannot completely account for individual differences in body proportions and shape.
Age and Development
Age itself is not always a direct variable in adult BSA formulas, but it matters when considering growth and body proportions, particularly in children.
Formula Selection
The equation used can affect the calculated BSA.
That’s why clinical protocols should specify the appropriate formula when BSA is used for treatment or dosing.
Who Should Use a BSA Calculator?
A BSA Calculator can be useful for:
- Medical students
- Nursing students
- Pharmacy students
- Healthcare professionals
- Researchers
- Healthcare educators
- People learning how BSA works
- Patients reviewing medical information
For general users, the calculator can be useful for understanding a laboratory or medical report.
However, patients should not use an online BSA estimate to make medication, chemotherapy, or other treatment decisions.
Frequently Asked Questions
What is a body surface area calculator?
A body surface area calculator estimates the body’s external surface area from measurements such as height and weight. The result is usually expressed in square meters.
How is body surface area calculated?
One commonly used method is the Mosteller formula:
BSA = √[(Height in cm × Weight in kg) ÷ 3600]
What is the Mosteller formula?
The Mosteller formula is:
BSA (m²) = √[(Height in cm × Weight in kg) ÷ 3600]
It was published as a simplified method for estimating body-surface area.
What is the Du Bois formula?
The Du Bois and Du Bois equation is:
BSA = 0.007184 × Height^0.725 × Weight^0.425
It is one of the earliest widely referenced BSA equations.
What is a normal body surface area?
There is no universal normal BSA.
BSA depends largely on body size and is not a health score.
What is BSA measured in?
BSA is normally measured in:
m², or square meters.
Why is BSA used in medicine?
BSA can be used to index certain physiological measurements and as part of some medication-dosing protocols. It is also relevant to cardiac index and standardized kidney-function reporting.
Is BSA the same as BMI?
No.
BSA estimates external body surface area. BMI relates body weight to height and is mainly used as a weight-status screening measure.
How accurate is a BSA calculator?
It is an estimate. Different formulas may produce slightly different results, especially in people at unusual heights or weights.
Why is BSA used for medication dosing?
Some medications, particularly certain chemotherapy treatments, use doses expressed per square meter of BSA. The actual dose must be determined using the relevant clinical protocol.
Can BSA be used for children?
Yes, BSA equations can be used in pediatric medicine, but the appropriate equation may differ by age and clinical purpose. The Haycock equation, for example, was developed across a population ranging from premature infants to adults.
What is the average adult body surface area?
There is no single adult BSA that applies to everyone. Values vary with height and weight.
Does BSA change with weight loss?
Yes. Because BSA calculations generally incorporate body weight, substantial weight changes can change the estimated BSA.
What is the difference between BSA and body weight?
Body weight measures mass. BSA estimates external body surface area.
Can BSA replace BMI?
No. They serve different purposes and should not be treated as interchangeable.
Is BSA used in kidney function?
Yes. BSA is relevant because eGFR is conventionally normalized to 1.73 m². BSA and eGFR, however, measure different things.
Related Calculators
- GFR Calculator
- Blood Pressure Calculator
- Blood Sugar Calculator
- BMI Calculator
- Body Fat Calculator
- Ideal Weight Calculator
- Lean Body Mass Calculator
- Calorie Calculator
Key Takeaways
- A Body Surface Area Calculator estimates the body’s external surface area using measurements such as height and weight.
- BSA is generally reported in m².
- The Mosteller formula is a simple and commonly used BSA equation.
- Du Bois and Haycock are other established BSA equations.
- BSA and BMI are different measurements with different clinical purposes.
- BSA can be used in some medication-dosing protocols, cardiac-index calculations, and kidney-function measurements.
- Different BSA formulas can produce different results, particularly at some extremes of height and weight.
- An online BSA calculator should not be used independently to determine medication or chemotherapy doses.
References
- Mosteller RD. Simplified calculation of body-surface area. New England Journal of Medicine. 1987.
PubMed: Mosteller Formula - Du Bois D, Du Bois EF. A formula to estimate the approximate surface area if height and weight be known.
PubMed: Du Bois Formula - Haycock GB, Schwartz GJ, Wisotsky DH. Geometric method for measuring body surface area: a height-weight formula validated in infants, children, and adults. Journal of Pediatrics. 1978.
PubMed: Haycock Formula - Shuter B, Aslani A. Body surface area: Du Bois and Du Bois revisited. European Journal of Applied Physiology. 2000.
PubMed: BSA Formula Review - National Library of Medicine / StatPearls. Body Surface Area.
NCBI Bookshelf: Body Surface Area - Body Surface Area Formula Comparison Research. Comparison of two different formulas for body surface area in adults at extremes of height and weight.
PubMed: Mosteller vs Du Bois
Medical Disclaimer
This Body Surface Area Calculator provides an educational estimate based primarily on height and weight. It does not diagnose a medical condition and should not be used by itself to determine medication, chemotherapy, or other treatment doses.
When BSA is used in clinical decision-making, healthcare professionals should use the appropriate formula, laboratory information, prescribing guidance, and patient-specific factors.
Author Box
Written by: Suvojit Datta, M.Pharm
Last reviewed: August 2026