BSA Calculator
Mosteller is a commonly used general-purpose formula. Other formulas are provided for comparison.
BSA is an estimate derived from height and weight, not a direct measurement. Different equations may produce different results, particularly in children or people with unusual body proportions. This tool is for educational use and should not independently determine medication doses, chemotherapy doses, or clinical treatment decisions.
What Is a BSA Calculator?
A BSA calculator estimates Body Surface Area, which is the total external surface area of the human body. The result is usually expressed in square meters (m²) and is calculated using measurements such as height and weight.
Body Surface Area is commonly used in healthcare to standardize certain physiological measurements and support specific medical calculations. It is particularly relevant in oncology, pediatrics, cardiology, and clinical research.
You can also use this DA Calculator.
Measuring the body's entire surface directly is difficult. Instead, healthcare professionals use mathematical formulas that estimate BSA from readily available measurements. The Mosteller and Du Bois formulas are among the commonly used methods. Although they use the same height and weight inputs, their mathematical approaches differ slightly.
How to Use the Online BSA Calculator
You can estimate your body surface area by entering basic body measurements.
- Enter your body weight in kilograms or pounds.
- Enter your height in centimeters or feet and inches.
- Select a calculation formula if the tool provides multiple methods.
- Click Calculate to estimate your BSA.
- Review the result in square meters.
For example, someone who weighs 70 kg and measures 175 cm tall has an estimated BSA of approximately 1.85 m² using the Mosteller formula. Different formulas may produce slightly different results for the same person.
BSA Calculator Formula
Several mathematical equations are used to estimate body surface area. Most formulas use height and weight, although their coefficients and exponents vary.
Mosteller Formula
The Mosteller equation is widely used because it is simple and requires only two measurements.
BSA (m²) = √[(Height in cm × Weight in kg) ÷ 3600]
Where:
- BSA: Body Surface Area in square meters.
- Height: Body height in centimeters.
- Weight: Body weight in kilograms.
Example Calculation
Suppose a person has:
- Height: 170 cm
- Weight: 65 kg
Apply the formula:
BSA = √[(170 × 65) ÷ 3600]
BSA = √(11050 ÷ 3600)
BSA = √3.0694
BSA ≈ 1.75 m²
This is an estimate of the person's body surface area, not a direct physical measurement.
Du Bois BSA Formula
The Du Bois and Du Bois equation is another established method for estimating body surface area.
BSA (m²) = 0.007184 × Weight^0.425 × Height^0.725
Weight must be entered in kilograms and height in centimeters.
Example Calculation
For someone weighing 65 kg and measuring 170 cm:
BSA = 0.007184 × 65^0.425 × 170^0.725
BSA ≈ 1.75 m²
The Du Bois method uses different exponents from the Mosteller method. As a result, the two equations may give slightly different estimates, particularly at unusual combinations of height and weight. The formula selected for a clinical calculation should match the requirements of the relevant medical protocol.
Mosteller vs Du Bois BSA Calculator
Both formulas estimate the same physical quantity, but they use different mathematical relationships.
| Feature | Mosteller | Du Bois |
|---|---|---|
| Required inputs | Height and weight | Height and weight |
| Output | Square meters | Square meters |
| Calculation | Square root formula | Power-based formula |
| Common applications | General clinical and pediatric calculations | General clinical calculations |
| Main advantage | Simple calculation | Established historical formula |
Neither formula directly measures the body's surface. The most appropriate method depends on the clinical setting, patient characteristics, and applicable professional guidance.
Other Body Surface Area Formulas
Researchers have developed several additional equations for estimating BSA.
In the formulas below, W represents weight in kilograms, H represents height in centimeters, and BSA is expressed in square meters.
Haycock Formula
BSA = 0.024265 × W^0.5378 × H^0.3964
The Haycock equation was developed using measurements from infants, children, and adults. It is one of the formulas considered in pediatric settings.
Gehan and George Formula
BSA = 0.0235 × W^0.51456 × H^0.42246
This formula is another established height-and-weight method used in body surface area research and clinical calculations.
Fujimoto Formula
BSA = 0.008883 × W^0.444 × H^0.663
The Fujimoto equation was developed from anthropometric research involving Japanese populations.
Takahira Formula
BSA = 0.007241 × W^0.425 × H^0.725
This equation is similar in structure to the Du Bois formula but uses a different coefficient.
Different formulas may produce different BSA values. These differences matter when a calculation is being used for a clinical decision.
Average Body Surface Area by Age
Body surface area generally increases as children grow and varies with height, weight, and body proportions.
The following figures are approximate reference examples rather than individual clinical standards.
| Age or Group | Approximate BSA |
|---|---|
| Newborn | 0.25 m² |
| 2-year-old child | 0.50 m² |
| 10-year-old child | 1.14 m² |
| Adult female | 1.60 m² |
| Adult male | 1.90 m² |
Actual values can differ substantially between individuals within the same age group.
For personal calculations, measured height and weight provide a more useful estimate than a population average.
BSA Calculator for Pediatric Patients
Body surface area is frequently used in pediatric medicine because children's body sizes vary significantly as they grow.
A pediatric BSA calculation generally requires the child's current height and weight. For example, consider a child who weighs 20 kg and measures 115 cm tall.
Using the Mosteller formula:
BSA = √[(115 × 20) ÷ 3600]
BSA = √0.6389
BSA ≈ 0.80 m²
This estimate may be relevant when a pediatric treatment protocol specifically requires BSA. However, not every pediatric medicine is prescribed using body surface area. Many medicines use weight-based dosing, age-specific guidance, or other clinical criteria. A child's medication dose should never be determined from a general BSA estimate without the appropriate prescribing instructions and clinical verification.
BSA Calculator for Chemotherapy
Body surface area is used in the dosing of certain chemotherapy medicines. Some oncology treatment protocols express a prescribed dose in milligrams per square meter (mg/m²).
The general mathematical relationship is:
Calculated Dose (mg) = Prescribed Dose (mg/m²) × BSA (m²)
For example, if a protocol specifies 50 mg/m² and the patient's BSA is 1.80 m², the unadjusted mathematical amount would be:
50 × 1.80 = 90 mg
This example demonstrates unit conversion only. It is not a recommended dose for any medicine.
Actual chemotherapy prescribing is more complex. Depending on the drug and protocol, clinicians may consider kidney function, liver function, blood counts, treatment history, toxicity, dose limits, and other patient-specific factors. Some chemotherapy medicines use entirely different dosing methods.
Chemotherapy doses must be calculated, reviewed, and approved by qualified oncology professionals. A general-purpose calculator cannot establish a safe or appropriate treatment dose.
Difference Between BSA and BMI
Body Surface Area and Body Mass Index are different measurements. BSA estimates the body's external surface area. BMI describes the relationship between body weight and height squared.
BMI Formula
BMI = Weight (kg) ÷ Height (m)²
For example, a person weighing 70 kg and measuring 1.75 meters tall has:
BMI = 70 ÷ 1.75²
BMI ≈ 22.86 kg/m²
Using the Mosteller equation, the same person's BSA is approximately 1.84 m².
| Measurement | BSA | BMI |
|---|---|---|
| What it estimates | Body surface area | Weight relative to height |
| Typical unit | m² | kg/m² |
| Main inputs | Height and weight | Height and weight |
| Common use | Selected clinical calculations | Weight-status screening |
| Measures body fat directly? | No | No |
Neither BSA nor BMI directly measures body fat percentage.
BSA Calculations for Dogs and Cats
Veterinary medicine also uses body surface area in certain treatment protocols. However, human BSA equations should not automatically be applied to animals. Dogs and cats have different body proportions, and veterinary calculations commonly use species-specific equations based on body weight.
Veterinary oncology may use BSA-based dosing for certain medicines, but dose selection also depends on the animal's species, condition, treatment protocol, and other clinical factors. Pet owners should rely on a veterinarian for medication calculations rather than using a human body surface area estimate.
Why Is Body Surface Area Important?
BSA is used in several medical and research applications.
Clinical Pharmacology
Some medication protocols use body surface area as one factor in dose calculations.
Cardiology
Cardiac index relates cardiac output to body surface area.
The formula is:
Cardiac Index = Cardiac Output ÷ BSA
The result is typically expressed in liters per minute per square meter.
Pediatric Healthcare
Body surface area can help standardize certain clinical measurements across children of different sizes.
Kidney Function Reporting
Estimated glomerular filtration rate is often reported normalized to a standard body surface area of 1.73 m². In some clinical situations, the patient's actual BSA is used to convert a normalized result into an absolute estimate.
Medical Research
Researchers may use BSA to compare selected physiological measurements between participants of different body sizes.
Limitations of BSA Calculations
Although BSA formulas are widely used, they have several limitations.
- They estimate surface area rather than measuring it directly.
- Different equations can produce different results.
- Accuracy may vary at extremes of height, weight, or body composition.
- Height and weight alone do not describe organ function or medication clearance.
- BSA-based medication dosing does not eliminate the risk of adverse effects.
- Pediatric and veterinary applications may require specialized formulas or protocols.
Body surface area is one clinical measurement among many. It should not be used as a substitute for individualized medical assessment.
Frequently Asked Questions
What is the easiest formula for calculating BSA?
The Mosteller formula is one of the simplest methods:
BSA = √[(Height in cm × Weight in kg) ÷ 3600]
It requires only height and weight.
What is a normal BSA for adults?
Approximate reference values are around 1.6 m² for adult women and 1.9 m² for adult men, but individual measurements vary widely. There is no single normal value suitable for everyone.
Can I calculate BSA using pounds and inches?
Yes. Convert pounds into kilograms and inches into centimeters before applying formulas that require metric inputs.
One pound equals approximately 0.45359237 kg, and one inch equals exactly 2.54 cm.
Is BSA more accurate than BMI?
BSA and BMI measure different things, so neither is universally more accurate. BSA estimates surface area, while BMI describes weight relative to height.
Can BSA be used to calculate chemotherapy doses?
Certain chemotherapy protocols use BSA as part of dose calculations. However, the final prescribed dose requires professional assessment and verification.
Which BSA formula is best for children?
The Mosteller and Haycock equations are among the formulas used in pediatric contexts. The appropriate choice depends on the clinical application and its specified protocol.
Calculate Your Body Surface Area
Use the calculator above to estimate your body surface area from height and weight. You can compare commonly used formulas, including Mosteller and Du Bois, to understand how the results may differ.
BSA is useful for educational purposes and selected healthcare calculations, but the estimate alone cannot determine a diagnosis or medication dose. Always follow the applicable clinical protocol and professional medical guidance when using BSA in patient care.