BSA Calculator
Calculate BSA using all 8 clinical formulas with medication dosing, cardiac index, and burn fluid resuscitation modules
Required for the Schlich formula which uses gender-differentiated equations
Enter height in centimeters (metric) or feet and inches (imperial)
Enter your current body weight
Enter Your Measurements
Enter height and weight above to calculate body surface area using all 8 clinical formulas simultaneously.
How to Use the BSA Calculator
Enter Height, Weight, and Gender
Select your preferred unit system (metric or imperial), then enter your height and weight. Choose your gender to enable the Schlich formula, which uses separate equations for men and women. Results update automatically as you type — no need to click Calculate.
Review the 8-Formula Comparison
The main results panel shows your BSA calculated by all 8 validated clinical formulas simultaneously, along with a visual bar chart showing the spread between formulas. The Mosteller formula is highlighted as the recommended clinical standard. For pediatric patients, focus on the Haycock result. For East Asian patients, consider the Fujimoto or Takahira values.
Use the Clinical Modules
Switch between the four tabs to access specialized modules. The Medication tab calculates total drug doses from mg/m² inputs, with an optional dose cap at 2.2 m². The Cardiac tab calculates cardiac index from cardiac output or stroke volume and heart rate. The Burns tab uses the Rule of Nines checkbox estimator plus Parkland/Brooke formulas for 24-hour fluid resuscitation planning.
Interpret Results with Clinical Context
Compare your calculated BSA against the age and gender reference values table to understand where you fall relative to population norms. The BSA category indicator (Low/Normal/High) provides quick context. Use the print button to generate a formatted results sheet for clinical documentation or consultation.
Frequently Asked Questions
Which BSA formula should I use?
The Mosteller formula is the recommended choice for most clinical situations due to its mathematical simplicity and well-validated accuracy. It is the most widely used formula in modern oncology, pharmacy, and general medicine. For pediatric patients — especially neonates, infants, and children under 12 — the Haycock formula is the preferred choice because it was specifically validated for this population. For East Asian patients, the Fujimoto formula may provide better accuracy. The Schlich formula is the most modern option and incorporates gender differences, making it potentially more accurate for calculating individual-specific BSA. When in doubt, many institutions report the Mosteller value as the primary result while using the full formula comparison to confirm consistency.
What is a normal BSA for an adult?
The standard reference adult BSA is 1.73 m², which corresponds to a 70 kg, 170 cm person. However, normal adult BSA actually varies considerably by sex and body size. The average BSA for adult men is approximately 1.90 m², while the average for adult women is approximately 1.60 m². Clinical reference ranges define Low BSA as below 1.5 m², Normal as 1.5 to 2.5 m², and High as above 2.5 m². Tall or large-framed individuals commonly have BSAs of 2.0 to 2.3 m². The 1.73 m² reference value is important in nephrology because eGFR equations are normalized to this value — this is why eGFR is reported in mL/min/1.73 m² rather than raw mL/min.
Why do different formulas give different results?
Each BSA formula was derived from a different sample population using different measurement techniques. The Du Bois formula was derived from only 9 subjects in 1916, while the Gehan and George formula used 401 subjects in 1970. The Schlich formula used modern 3D surface scanning technology on a large German population in 2010. Because body proportions vary between ethnic groups and have changed over time with population-level changes in height and weight, no single formula is universally most accurate. For most average-sized adults, the formulas agree within 2 to 3 percent. The largest differences occur at the extremes — very obese patients, very tall individuals, neonates, and patients with unusual body proportions.
How is BSA used for chemotherapy dosing?
Cytotoxic chemotherapy drugs are almost universally dosed in milligrams per square meter (mg/m²) of body surface area. This approach normalizes drug exposure for patients of different body sizes and minimizes the risk of under-dosing (leading to treatment failure) or over-dosing (leading to toxicity). For example, a drug prescribed at 100 mg/m² would be given as 170 mg to a patient with a BSA of 1.70 m². A significant controversy in oncology is whether obese patients should receive full BSA-based doses or whether BSA should be capped at 2.2 m². Some evidence suggests that dose capping in obese patients leads to subtherapeutic drug levels, while the historical rationale for capping was to prevent toxicity. Current guidelines generally recommend full BSA-based dosing for most chemotherapy regimens in obese patients.
What is cardiac index and why does it use BSA?
Cardiac index (CI) is cardiac output normalized to body surface area, expressed in liters per minute per square meter (L/min/m²). A large person naturally has a higher absolute cardiac output than a small person simply because they need to supply blood to more tissue. Comparing raw cardiac output values between patients of different sizes is therefore misleading. Dividing by BSA yields a standardized value that can be compared across patients. The normal range for cardiac index is 2.5 to 4.0 L/min/m². Values below 2.0 L/min/m² indicate cardiogenic shock and typically require immediate intervention. Values above 4.0 L/min/m² indicate a hyperdynamic state, which can occur in sepsis, hyperthyroidism, severe anemia, pregnancy, or during exercise.
How does the Rule of Nines help estimate burns?
The Rule of Nines is a simple method for estimating the percentage of total body surface area (TBSA) affected by burns. The body is divided into regions each representing 9% of total BSA or multiples thereof: the head and neck account for 9%, each arm accounts for 9%, the anterior trunk (chest and abdomen) accounts for 18%, the posterior trunk (upper and lower back) accounts for 18%, each leg accounts for 18%, and the perineum accounts for 1%, totaling 100%. Once TBSA% is estimated, the Parkland formula (4 mL × weight in kg × TBSA%) calculates the total crystalloid fluid required in the first 24 hours. Half is given in the first 8 hours and the remaining half over the next 16 hours. Our calculator includes interactive checkboxes for each body region so you can estimate TBSA% directly in the tool.