Your body surface area (BSA) is an estimate of the total outer surface of your body, measured in square meters (m²). Clinicians use BSA to personalize drug dosing, assess cardiac output, and estimate burn coverage. Enter your height and weight into the calculator above to get your result in seconds.
The average adult BSA falls roughly between 1.7 and 2.0 m². Your specific number depends on your height, weight, and which formula is applied. This calculator uses the Du Bois formula by default, the most commonly used BSA formula in clinical medicine.
BSA is not a diagnostic tool. Use your result as a planning estimate and discuss medication or treatment decisions with a healthcare provider.
Calculate Your Body Surface Area (BSA)
To calculate your body surface area, you need two measurements: your height and your weight. That's it.
- Step on a scale and record your weight in kilograms or pounds.
- Measure your height in centimeters or inches.
- Enter both values into the calculator above.
The tool returns your estimated BSA in square meters. It also shows results from several well known formulas so you can compare.
Most adults see a BSA between 1.5 m² and 2.2 m². Women typically fall in the range of 1.6 to 1.8 m², while men commonly range from 1.8 to 2.1 m². These are general reference points, not strict categories.
How the BSA Calculation Works
Every BSA formula estimates the approximate surface area of a human body using height and weight. No formula measures skin directly. Instead, each one applies a mathematical model validated against physical measurements taken from study participants.
The basic idea: taller and heavier people have more surface area. Each formula weights height and weight slightly differently, which is why results can vary by a small margin depending on which equation you choose.
The calculator applies the height and weight you provide to an exponential equation. It raises each value to a specific power, multiplies them, and then scales the product by a constant. The output is your estimated BSA in m².
Du Bois Formula for Body Surface Area
The original Du Bois and DuBois formula
In 1916, Du Bois EF and Du Bois D published a geometric method for measuring body surface area. Their formula remains the most widely cited BSA equation in medicine over a century later.
The Du Bois formula:
BSA (m²) = 0.007184 × height (cm)^0.725 × weight (kg)^0.425
The original study measured only nine subjects, which is a frequently noted limitation. Despite the small sample, the formula has been validated repeatedly in children and adults across clinical settings.
This is the default formula in most medical calculators, including this one. If a drug label or clinical protocol references "BSA" without specifying a formula, it almost always means Du Bois.
Other BSA formulas used in clinical medicine
Several alternative equations exist. Each was developed to address perceived gaps in the Du Bois formula or to improve accuracy for specific populations.
- Mosteller (1987): BSA = √(height (cm) × weight (kg) / 3600). Simple to compute by hand. Widely used in pediatrics and oncology.
- Haycock GB et al. (1978): A height-weight formula validated in infants and children. Often preferred in pediatric dosing.
- Boyd (1935): Uses a more complex logarithmic approach. Less commonly applied today.
- Gehan and George (1970): Developed from a larger dataset than Du Bois. Sometimes used in chemotherapy protocols.
In practice, results from these formulas usually fall within 5% to 10% of each other for normal-weight adults. Differences become more meaningful at the extremes of body size. The calculator shows results from multiple formulas so you can compare.
How to Calculate BSA for Dosage
Many medications, especially in oncology, are dosed per square meter of body surface area. BSA-based dosing attempts to account for differences in metabolic mass between patients, rather than relying on weight alone.
The basic dosage calculation:
Dose = prescribed dose per m² × patient's BSA
For example, if a drug is prescribed at 150 mg/m² and the patient's BSA is 1.8 m², the calculated dose is 270 mg.
This is an estimate to support understanding. Actual prescribing involves clinical judgment, lab values, organ function, and protocol-specific adjustments.
Chemotherapy dosage and patient BSA
Chemotherapy dosage is the most common clinical use of BSA. Oncologists use BSA to personalize drug doses because cancer treatments often have a narrow therapeutic index. Too little may be ineffective. Too much increases toxicity.
Standard chemotherapy protocols list doses in mg/m². The treating team calculates the patient's BSA before each cycle, since weight can change during treatment.
Some oncology guidelines cap BSA at 2.0 m² for dose calculations, while others dose based on actual BSA regardless of body size. Protocol specifics vary by cancer type and drug regimen.
Drug dosage for pediatric patients
Pediatric dosing relies heavily on BSA because children vary enormously in size relative to age. Weight-based dosing (mg/kg) is also used, but BSA-based dosing can be more accurate for certain medications.
For infants and small children, the Haycock or Mosteller formula is often preferred over Du Bois. The Haycock formula (Haycock GB, Schwartz GJ, Wisotsky DH, 1978) was specifically validated in infants and young children, where the Du Bois equation may be less reliable.
Pediatric oncology, fluid resuscitation, and certain IV medications commonly reference BSA. Always follow the specific dosing protocol and confirm calculations with the prescribing clinician.
Body Surface Area vs Body Mass Index (BMI)
BSA and BMI both use height and weight, but they measure fundamentally different things.
| BSA | BMI | |
|---|---|---|
| What it estimates | Total surface area of the body (m²) | Ratio of weight to height squared (kg/m²) |
| Primary use | Drug dosing, cardiac output, burn assessment | Screening for overweight and obesity |
| Output | Area in square meters | Dimensionless number |
BMI tells you whether someone's weight is proportional to their height. BSA tells you how much external surface their body has. A person can have a normal BMI but an above-average BSA if they are tall.
When to use a BSA calculator vs a BMI calculator
Use a BSA calculator when you need a surface area estimate for clinical purposes: medication dosing, cardiac index, or burn coverage.
Use a BMI calculator when you want a quick screening of body weight relative to height. BMI is commonly used for general health assessment, identifying risk factors for heart disease, and tracking weight changes over time.
They are complementary tools, not interchangeable. If your goal is to understand a drug dose, BSA is the relevant number. If your goal is to assess body fat category, BMI is the standard starting point (though it has its own well-known limitations, such as not distinguishing muscle from fat).
BSA and the Cardiac Index
The cardiac index measures how well the heart pumps blood relative to body size. It is calculated by dividing cardiac output (liters per minute) by BSA (m²).
Cardiac Index = Cardiac Output ÷ BSA
A normal cardiac index is roughly 2.5 to 4.0 L/min/m². Values below 2.2 L/min/m² may indicate reduced cardiac function.
Without BSA, raw cardiac output numbers are hard to compare between a small person and a large one. BSA normalizes the measurement, giving clinicians a standardized way to assess heart performance across patients of different sizes.
Cardiac index is used in critical care, cardiology, and internal medicine. If you've been asked to know your BSA for a cardiac evaluation, this calculator provides the estimate you need.
Body Surface Area in Burn Estimation
Burn centers use body surface area to determine how much skin has been damaged. The total body surface area (TBSA) affected by a burn directly guides fluid resuscitation and treatment decisions.
The most common method is the "Rule of Nines," which divides the adult body into regions each representing roughly 9% (or multiples of 9%) of total surface area:
- Head and neck: 9%
- Each arm: 9%
- Chest (front): 18%
- Back: 18%
- Each leg: 18%
- Groin: 1%
For children, the Lund and Browder chart is more accurate because body proportions differ from adults.
Knowing your calculated BSA in m² is helpful context, but burn percentage estimation is a separate clinical assessment performed by medical professionals. This calculator estimates your total BSA. It does not assess burn percentage.
BSA Formula Limitations for Obese Patients
Most BSA formulas, including Du Bois, were developed using data from normal-weight or moderately overweight individuals. Their accuracy decreases in obese adults.
The core problem: as body weight increases substantially, the relationship between weight and surface area changes. Excess adipose tissue does not add surface area at the same rate that lean tissue does. This means BSA formulas can overestimate the actual surface area in patients with obesity.
For drug dosing, overestimation of BSA in obese patients can lead to higher calculated doses. With medications that have a narrow therapeutic index (like many chemotherapy agents), this raises the risk of toxicity. Some clinical protocols address this by:
- Capping BSA at a set value (commonly 2.0 m²)
- Using adjusted or ideal body weight instead of actual weight
- Applying obesity-specific dosing guidelines
No single formula performs consistently well across all levels of obesity. BSA measurements in this population should be interpreted with caution, and dosing decisions should always involve clinical oversight.
Frequently Asked Questions About the Body Surface Area Calculator
How do I calculate my body surface area? Enter your height and weight into the calculator at the top of this page. The tool applies the Du Bois formula (and several others) to estimate your BSA in square meters. No other measurements are needed.
What is a normal BSA for a woman? Most women have a BSA between approximately 1.6 and 1.8 m². This varies with height and weight. There is no single "normal" value, just a typical range.
What is the most common BSA formula? The Du Bois and DuBois formula from 1916 is the most commonly used BSA formula in clinical medicine. The Mosteller formula is also popular because of its simplicity.
What do my body surface area results mean? Your BSA is a surface area estimate in square meters. By itself, it is not a health score or a diagnosis. It is used as an input for clinical calculations like drug dosing, cardiac index, and burn assessment. If your BSA was requested for a specific medical reason, share the result with your provider.
Can I use this calculator for children? Yes. Enter the child's height and weight, and the calculator will return a BSA estimate. For infants and young children, the Haycock or Mosteller formula may be more appropriate than Du Bois. The calculator displays results from multiple formulas for comparison.
Is BSA the same as BMI? No. BSA estimates the total surface area of your body in square meters. BMI is a ratio of weight to height used to screen for overweight and obesity. They use the same inputs but answer different questions.
Why is BSA used instead of weight alone for drug dosing? BSA correlates more closely with metabolic mass and organ size than weight alone does. This makes it a better predictor of how a patient will process certain drugs, especially those with a narrow therapeutic index. That said, not all medications use BSA-based dosing.
How accurate is this calculator? The calculator applies published, peer-reviewed formulas accurately. The formulas themselves are estimates. Results from different formulas may vary by a few percent. For clinical treatment decisions, always verify calculations with your healthcare team.