Body Surface Area Calculator: BSA Formula and Clinical Applications
Calculate Body Surface Area (BSA) using the Mosteller, DuBois, and Haycock formulas. Covers why BSA is used for chemotherapy dosing, burn estimation, and pediatric medicine.
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What Body Surface Area Is
Body Surface Area (BSA) is the total measured or calculated surface of the human body. Unlike BMI, which only uses weight and height, BSA more accurately reflects metabolic mass and is used in clinical settings where dosing based on body surface provides better therapeutic outcomes.
BSA is expressed in square meters (m²). An average adult has a BSA of approximately 1.7–1.9 m².
Major BSA Formulas
Mosteller Formula (1987) — Most Widely Used: BSA (m²) = √(height in cm × weight in kg ÷ 3600)
Simplified: BSA = √(H × W) ÷ 60
DuBois and DuBois Formula (1916) — Historical Standard: BSA = 0.007184 × height^0.725 × weight^0.425
Haycock Formula (1978) — Preferred for Pediatric Patients: BSA = 0.024265 × height^0.3964 × weight^0.5378
Gehan-George Formula: BSA = 0.0235 × height^0.42246 × weight^0.51456
Worked Example
Patient: 170 cm height, 70 kg weight
Mosteller: √(170 × 70 ÷ 3600) = √3.306 = 1.82 m² DuBois: 0.007184 × 170^0.725 × 70^0.425 = 1.83 m² Haycock: 0.024265 × 170^0.3964 × 70^0.5378 = 1.82 m²
The formulas are in close agreement for adults of average build. Discrepancies increase for very tall/short, very light/heavy, or pediatric patients.
Clinical Applications of BSA
1. Chemotherapy Dosing Many chemotherapy agents are dosed in mg/m² of BSA because toxicity and efficacy correlate better with BSA than with body weight alone. Common examples: - Paclitaxel: 135–175 mg/m² - Carboplatin: dose is calculated using AUC × (GFR + 25) — BSA often involved in GFR calculation - Doxorubicin: 60–75 mg/m²
2. Burn Assessment Estimating the percentage of total body surface area (TBSA) burned determines fluid resuscitation needs. The Parkland formula for burns: - Fluid (mL) = 4 × weight (kg) × % TBSA burned - First 24 hours: half given in first 8 hours, remainder over next 16 hours
3. Cardiac Output Normalization Cardiac index = Cardiac output (L/min) ÷ BSA — normalizes cardiac output for body size. Normal range: 2.5–4.0 L/min/m²
4. Pediatric Medication Dosing For pediatric patients, BSA-based dosing adjusts for the non-linear relationship between weight and metabolic rate in children. The Haycock formula is preferred for pediatric BSA.
BSA vs. BMI
BSA accounts for actual surface area (relevant to heat exchange, transdermal absorption, drug distribution). BMI is simpler but doesn't reflect body composition or surface accurately. A muscular person with BMI 28 may have a lower BSA than a person with BMI 28 but more adipose tissue.
Normal BSA Reference Values
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Frequently Asked Questions
- How is body surface area calculated?
- The Mosteller formula is most widely used: BSA (m²) = √(height in cm × weight in kg ÷ 3600). For a 170 cm, 70 kg person: √(170 × 70 ÷ 3600) = √3.306 = 1.82 m². Other formulas (DuBois, Haycock, Gehan-George) produce similar results for average adults.
- Why is body surface area used for chemotherapy dosing?
- BSA-based dosing accounts for differences in drug distribution, metabolism, and clearance across different body sizes better than weight alone. Chemotherapy drugs have narrow therapeutic windows — underdosing reduces efficacy, overdosing causes excessive toxicity. BSA dosing produces more consistent drug exposure across patients.
- What is a normal body surface area?
- Average adult men: approximately 1.9 m². Average adult women: approximately 1.6 m². Newborns: ~0.25 m². A 12-year-old child: ~1.3 m². BSA scales with body size — taller and heavier individuals have larger BSA.
- Which BSA formula is most accurate?
- For adults of average build, Mosteller, DuBois, and Gehan-George produce similar results (within 2–3%). Haycock is preferred for pediatric patients. DuBois may slightly overestimate BSA in obese individuals. Mosteller is the most commonly used in clinical practice due to its simplicity.
- How is total body surface area used in burn treatment?
- Burn treatment uses % TBSA (percent of total body surface area burned) to determine severity and calculate IV fluid resuscitation using the Parkland formula: 4 mL × weight (kg) × % TBSA burned in the first 24 hours. Burns covering > 20% TBSA require hospitalization and IV fluid management.
Last updated 7/28/2026