What Is the Body Surface Area Calculator?
A nurse in an oncology ward needs to calculate the correct dose of carboplatin for a patient. She does not use the patient's weight alone. She uses body surface area, or BSA, measured in square meters. Getting this number right is the difference between a therapeutic dose and a toxic one.
BSA is the total surface area of the human body. It is used in medicine for chemotherapy dosing, burn severity assessment, cardiac output normalization, and kidney function estimation. This calculator computes BSA using three established formulas: DuBois, Mosteller, and Haycock. According to the StatPearls reference at the National Institutes of Health (updated February 2025), BSA was first used in the late 19th century when the German physiologist Max Rubner discovered that metabolic rate correlated better with body surface area than with body weight.
Inputs Required
- Weight: Your body weight in kilograms
- Height: Your height in centimeters
Outputs Provided
- Average BSA: The average of three formulas in m squared
- DuBois BSA: Result using the DuBois formula
- Mosteller BSA: Result using the Mosteller formula
- Haycock BSA: Result using the Haycock formula
How the Calculation Works
Three formulas are in widespread clinical use. The DuBois formula, published in 1916, is the oldest and most widely referenced. The Mosteller formula, introduced in 1987, is simpler and has become the preferred choice at many institutions. Cancer Care Ontario, for example, recommends using only the Mosteller formula for chemotherapy dosing to avoid confusion between systems. The Haycock formula, published in 1978, is often preferred for pediatric patients because it performs better at very low body weights.
DuBois: BSA = 0.007184 x Weight^0.425 x Height^0.725
Mosteller: BSA = sqrt((Weight x Height) / 3600)
Haycock: BSA = 0.024265 x Weight^0.5378 x Height^0.3964
Where Weight is in kg and Height is in cm
A 2017 study published in the Journal of Oncology Pharmacy Practice compared five validated BSA formulas and found that while differences exist, they are usually small enough to be clinically insignificant for most adults. The differences become more pronounced at extreme body sizes, which is why some institutions cap BSA at 2.2 or 2.3 m squared for dosing purposes.
How to Use the Calculator
- Enter your weight in kilograms
- Enter your height in centimeters
- View your BSA calculated using three different formulas
- Use the average or formula-specific result as needed
If you are tracking body composition more broadly, you may also want to check your BMI or Ideal Weight alongside BSA. For kidney function calculations that use BSA as an input, see our GFR Calculator.
Example Calculations
Example 1: Standard Adult Male
A person weighing 70 kg and 175 cm tall:
- DuBois: 0.007184 x 70^0.425 x 175^0.725 = 1.84 m squared
- Mosteller: sqrt((70 x 175) / 3600) = 1.85 m squared
- Haycock: 0.024265 x 70^0.5378 x 175^0.3964 = 1.86 m squared
- Average: 1.85 m squared
The three formulas agree within 0.02 m squared. For a chemotherapy drug dosed at 100 mg per m squared, this patient would receive 185 mg. The difference between using the DuBois and Haycock results is only 2 mg, which is clinically negligible.
Example 2: Pediatric Patient
A child weighing 14 kg and 95 cm tall:
- DuBois: 0.61 m squared
- Mosteller: 0.61 m squared
- Haycock: 0.63 m squared
- Average: 0.62 m squared
At very low body weights, the Haycock formula tends to produce slightly higher values than DuBois or Mosteller. This is why many pediatric oncology protocols specify which formula to use rather than leaving it to individual preference.
Real World Scenarios
Chemotherapy Dosing at a Cancer Center
Maria, a 58-year-old woman weighing 62 kg and 160 cm tall, is beginning a carboplatin regimen. Her oncologist calculates her BSA at 1.66 m squared using the Mosteller formula. The protocol calls for a dose of 400 mg per m squared, so Maria receives 664 mg per cycle. A 2021 study at the University of New Mexico Comprehensive Cancer Center found that switching the e-prescribing platform from DuBois to Mosteller changed chemotherapy doses for some patients by up to 3%, which was within the safe dosing range but highlighted the importance of institutional consistency.
Burn Severity Assessment in the ER
A 42-year-old construction worker arrives at the emergency department with second-degree burns on his torso and right arm. The medical team uses the Rule of Nines to estimate the percentage of BSA affected, which determines fluid resuscitation volumes using the Parkland formula. The total BSA calculation helps convert the percentage estimate into absolute surface area, which guides the liters of Lactated Ringer's solution needed in the first 24 hours.
Normalizing Cardiac Output Measurements
A cardiologist comparing two patients finds that Patient A has a cardiac output of 6.0 L/min and Patient B has 4.5 L/min. Without accounting for body size, Patient B appears to have lower cardiac function. But Patient A is 185 cm and 95 kg (BSA 2.18 m squared) while Patient B is 155 cm and 50 kg (BSA 1.52 m squared). When normalized to BSA, the cardiac index is 2.75 and 2.96 L/min/m squared respectively. Patient B actually has the higher cardiac index.
Why This Calculation Matters
BSA correlates better with metabolic mass than body weight alone. It accounts for both height and weight, which means a 60 kg person who is 150 cm tall and a 60 kg person who is 190 cm tall get different BSA values. This matters because drug clearance, cardiac output, and kidney function all scale with metabolic mass rather than raw weight.
For chemotherapy specifically, BSA-based dosing has been the standard for decades. The goal is to individualize the dose so that a smaller patient does not receive too much and a larger patient does not receive too little. Some newer protocols are moving toward flat dosing or weight-based dosing for certain drugs, but BSA remains the dominant approach for most oncology regimens.
Common Mistakes to Avoid
- Using different formulas inconsistently: If your institution uses Mosteller, do not switch to DuBois mid-treatment. A 2021 study at UNMCCC showed that switching formulas can change doses by up to 3%, which is usually safe but can matter for narrow-therapeutic-index drugs.
- Confusing BSA with BMI: BSA measures total surface area in square meters. BMI measures weight relative to height squared. They serve completely different purposes. BSA is for drug dosing and physiological normalization. BMI is for weight classification.
- Not capping BSA for obese patients: Some institutions cap BSA at 2.2 or 2.3 m squared for dosing because BSA formulas may overestimate metabolic mass in severely obese individuals. Check your institution's protocol.
- Using outdated measurements: If a patient loses or gains significant weight during treatment, recalculate BSA. A 10% weight change can alter the BSA enough to affect dosing.
Limitations of This Calculator
This tool provides an estimate based on population-derived formulas. It does not account for body composition differences such as muscle mass versus fat mass, which can affect drug distribution. The formulas were developed primarily on Western populations and may be less accurate for other ethnic groups. For pediatric patients, especially infants under 5 kg, the Haycock formula is generally preferred but even it has limited validation at extreme low weights. This calculator does not replace clinical judgment or institutional dosing protocols. Always consult the prescribing information and your institution's pharmacy team for dosing decisions.
Authoritative Research and Resources
- StatPearls: Body Surface Area (NIH) - The definitive clinical reference for BSA, updated February 2025. Covers the history, formula comparisons, and clinical applications including chemotherapy dosing, burn assessment, and cardiac index normalization.
- Not All Body Surface Area Formulas Are the Same, but Does It Matter? - A peer-reviewed study from the Journal of Oncology Pharmacy Practice comparing five validated BSA formulas and analyzing the clinical significance of their differences.
- Cancer Care Ontario: BSA Calculation Guideline - An institutional guideline recommending the Mosteller formula as the single standard for chemotherapy dosing to reduce variability and medication errors.
For related health calculations, try our BMI Calculator, Ideal Weight Calculator, or GFR Calculator.