Body Surface Area Calculator

  • Adam
  • November 1, 2025

Free body surface area calculator using Mosteller, DuBois, Boyd, and Gehan-George formulas. Calculate BSA for medication dosing, burn assessment, and medical applications.

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Body Surface Area (BSA) Calculator

Calculate your body surface area using multiple medical formulas. BSA is used for medication dosing, burn assessment, and other clinical applications. Accurate calculations with DuBois, Mosteller, Boyd, and Gehan-George methods.

📋 Quick Navigation

📐 Calculate your body surface area! 💪
in pounds (lbs)
feet
0-11 inches
in kilograms (kg)
in centimeters (cm)
Average Body Surface Area
TBD
m² (square meters)

Mosteller Formula

—
m²

DuBois Formula

—
m²

Boyd Formula

—
m²

Gehan-George

—
m²

📊 BSA Calculation Comparison

Formula BSA Result (m²) Year Developed Common Use
Mosteller — 1987 Most commonly used today
DuBois — 1916 Original formula, still widely used
Boyd — 1935 Pediatric and obese patients
Gehan-George — 1970 Pediatric oncology dosing

🧠 Understanding Body Surface Area

What is Body Surface Area (BSA)?

Body Surface Area is the total surface area of the human body measured in square meters (m²). Unlike body weight, BSA accounts for both height and weight proportionally, providing a better representation of body composition. The average adult BSA ranges from 1.5 to 2.5 m², with typical values around 1.7-2.0 m².

Why is BSA Important?

Medication Dosing: Many drugs, especially chemotherapy agents, are dosed based on BSA rather than weight to ensure appropriate drug concentration. Burn Assessment: Determining the percentage of BSA affected helps calculate fluid replacement needs and guides treatment urgency. Clinical Trials: BSA standardizes results across patients with different body sizes. Fitness Assessment: BSA is used in various fitness and athletic assessments.

Normal BSA Ranges by Age

Newborns: 0.25-0.35 m². Young children (2-10 years): 0.5-1.0 m². Adolescents (10-18 years): 1.0-1.7 m². Adults: 1.5-2.5 m² (most common 1.7-2.0 m²). Variation: BSA varies significantly based on individual height, weight, and body composition.

💊 Medical Note: Always consult with a healthcare provider for medication dosing. This calculator provides BSA estimates for educational purposes and should not be used independently for determining drug doses. Doctors may adjust calculations based on individual patient factors.

🧮 BSA Calculation Formulas

Mosteller Formula (Most Common)

BSA (m²) = √[(Height (cm) × Weight (kg)) / 3600]

OR in imperial units:
BSA (m²) = √[(Height (in) × Weight (lbs)) / 3131]

Example: 175 cm tall, 70 kg
BSA = √[(175 × 70) / 3600]
BSA = √[12250 / 3600]
BSA = √3.403
BSA = 1.84 m²

DuBois Formula (Original, 1916)

BSA (m²) = 0.007184 × Height (cm)^0.725 × Weight (kg)^0.425

OR:
BSA (m²) = 0.00007184 × Height (in)^0.725 × Weight (lbs)^0.425

Note: Most accurate for average adults

Boyd Formula (1935)

BSA (m²) = 0.03330 × Weight (kg)^(0.6157 - 0.0188 × log₁₀(Weight))
× Height (cm)^0.3

Note: Often used for obese and pediatric patients

Gehan-George Formula (1970)

BSA (m²) = 0.0235 × Height (cm)^0.42246 × Weight (kg)^0.51456

Note: Commonly used in pediatric oncology for chemotherapy dosing

💊 Medical Applications of BSA

Chemotherapy Dosing

Most chemotherapy drugs are dosed according to BSA. For example, a typical chemotherapy dose might be "1200 mg/m²", meaning the patient receives 1200 mg multiplied by their BSA in m². This ensures that regardless of patient size, they receive an appropriate drug concentration in their bloodstream. Dosing adjustments may be made for kidney or liver dysfunction.

Burn Severity Assessment

Healthcare providers use the "Rule of Nines" to estimate the percentage of BSA affected by burns. Total body water requirements and fluid replacement therapy are calculated based on BSA affected. For example, extensive burns affecting 40% of BSA may require significant fluid resuscitation calculated as: (% BSA burned × Body weight in kg) × 4 mL of crystalloid fluid over 24 hours.

Hydration Requirements

Daily fluid requirements are sometimes calculated using BSA, especially in pediatric patients or those with significant metabolic changes. The Holliday-Segar method uses BSA to determine total daily fluid needs. Healthcare providers may use this in intensive care settings or for patients with unusual fluid requirements.

Body Mass Index (BMI) Correlation

While BSA and BMI are different measurements, they're related. BMI uses height and weight to assess weight status. BSA provides a more complete picture of body size for medical purposes. A person with the same BMI but different height/weight distributions may have slightly different BSA values.

Cardiac Function Assessment

Cardiac output, ejection fraction, and other heart measurements are sometimes indexed to BSA for comparison across patients of different sizes. This helps physicians determine if cardiac function is appropriate for the patient's body size. Cardiac index (cardiac output / BSA) is used in clinical cardiology.

⚕️ Important: BSA calculations are tools used by healthcare providers. Never self-administer medications based on BSA calculations. Your doctor determines appropriate dosing based on BSA and other medical factors. Always follow professional medical advice.

❓ Frequently Asked Questions

Does BSA change with age? +
Yes, BSA changes with age. Infants and young children have smaller BSA (0.3-1.0 m²), while adults typically range from 1.5-2.5 m². BSA increases as children grow. In elderly patients, BSA may slightly decrease due to height loss and changes in body composition, but the change is usually minimal.
Why do different formulas give different results? +
Different BSA formulas were developed at different times using different populations. The Mosteller formula is simpler and widely used today. The DuBois formula (original from 1916) is still highly regarded. Results typically differ by only 5-10%, but for medication dosing, your healthcare provider specifies which formula to use.
Is my BSA at a healthy level? +
BSA itself isn't "healthy" or "unhealthy" - it's simply a measure of body surface area. However, BSA is used by doctors to assess if values are appropriate for your height, weight, and age. Discuss your BSA with your healthcare provider in context of your overall health, BMI, and fitness level.
How accurate is this BSA calculator? +
This calculator uses standard medical formulas and is accurate for height/weight inputs. However, actual BSA can vary based on body composition, age, and individual factors. For medication dosing, always consult your healthcare provider who may adjust calculations based on your specific medical situation.
Can BSA be used for exercise and fitness? +
Yes, BSA is sometimes used in fitness assessments, athletic performance evaluation, and exercise science. However, BMI, body composition, and fitness level are more commonly used for fitness purposes. BSA is primarily a medical measurement used for medication dosing and clinical assessments.
Should I use metric or imperial units? +
Use whichever system you're most comfortable with - both produce the same result. Healthcare providers typically use metric units (cm, kg) in clinical settings. The calculator provides both options for your convenience. Choose whichever matches your available measurements.
Is gender important for BSA calculation? +
Most modern formulas (like Mosteller) don't differentiate by gender - height and weight determine BSA regardless of gender. However, some specialized formulas or medical contexts may use gender-specific calculations. For standard BSA estimation, gender is less critical than accurate height/weight measurements.

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