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Calculate BSA using medically validated formulas for accurate clinical applications.
Calculate BSA using various medical formulas
Everything you need to know
Body Surface Area (BSA) is a measurement of the total skin surface area of a human body, expressed in square meters (m²). While not directly used in fitness training, BSA is a critical metric in medical practice used for:
Four main formulas are used to calculate BSA, each developed through different research populations.
Our BSA calculator determines your body surface area using multiple formulas:
Enter Your Height
Enter Your Weight
View BSA Estimates
Understand Clinical Applications
The Mosteller formula is the simplest and most widely used in modern clinical practice.
Formula:
BSA (m²) = √ [Height (cm) × Weight (kg) ÷ 3600]
Or in imperial units:
BSA (m²) = √ [Height (in) × Weight (lbs) ÷ 3131]
Advantages:
Example: 70 kg person, 180 cm tall
The Du Bois formula was the first widely used BSA formula and remains standard in some contexts.
Formula:
BSA (m²) = 0.007184 × Weight (kg)^0.425 × Height (cm)^0.725
Advantages:
Example: 70 kg person, 180 cm tall
The Haycock formula was specifically developed for pediatric (child) patients.
Formula:
BSA (m²) = 0.024265 × Weight (kg)^0.5378 × Height (cm)^0.3964
Advantages:
Example: 15 kg child, 100 cm tall
The Gehan & George formula was developed through extensive research in patient populations.
Formula:
BSA (m²) = 0.010 × Weight (kg)^0.67 × Height (cm)^0.33
Advantages:
Example: 70 kg person, 180 cm tall
| Formula | Best Use | Accuracy | Notes |
|---|---|---|---|
| Mosteller | General population, most common | Very good | Simplest, preferred for routine use |
| Du Bois | Historical comparisons, adults | Very good | Original formula, still widely used |
| Haycock | Pediatric patients | Very good | Specifically validated for children |
| Gehan & George | Research, specific populations | Good | Based on extensive empirical data |
Key Point: For most clinical applications, Mosteller and Du Bois produce nearly identical results in adults (within 2-5% difference). The choice between them rarely affects clinical decisions.
| BSA Range | Classification | Typical Patient |
|---|---|---|
| < 0.5 m² | Very small | Newborn infants |
| 0.5-1.0 m² | Small | Infants, young children |
| 1.0-1.5 m² | Medium | Children, small adolescents |
| 1.5-2.0 m² | Large | Adolescents, small adults |
| 2.0-2.5 m² | Very large | Average to large adults |
| > 2.5 m² | Extremely large | Large adults, obese individuals |
Many chemotherapy drugs and some other medications are dosed based on BSA rather than body weight because it provides more accurate dosing across different body sizes.
Example: Chemotherapy Dosing
A drug prescribed at 100 mg/m²:
Why use BSA?
BSA is used to calculate several important cardiac metrics:
Cardiac Index:
Cardiac Index = Cardiac Output (L/min) ÷ BSA (m²)
Normal: 2.5-4.0 L/min/m²
This standardizes heart function across different patient sizes.
In severe burn cases, BSA of burned skin determines fluid resuscitation strategy (Parkland formula):
24-hour fluid (mL) = 4 × BSA burned (m²) × Weight (kg)
Example: 30 kg child with 50% BSA burn (BSA = 1.0 m²)
A more body-composition-independent estimate of metabolic rate:
Resting Metabolic Rate ≈ 3,500 × BSA (kcal/day)
This is more accurate than some weight-based formulas for obese individuals.
Key insight: Two people of the same weight and height have the same BSA regardless of body composition (muscle vs. fat), which is why BSA is so useful for standardizing medical dosing.
| Age/Weight | Height | Haycock BSA |
|---|---|---|
| Newborn (3.5 kg) | 50 cm | 0.23 m² |
| 6 months (7 kg) | 67 cm | 0.41 m² |
| 1 year (10 kg) | 75 cm | 0.49 m² |
| 3 years (14 kg) | 95 cm | 0.60 m² |
| 5 years (18 kg) | 109 cm | 0.72 m² |
| 10 years (32 kg) | 138 cm | 1.05 m² |
| 15 years (55 kg) | 170 cm | 1.60 m² |
Dose: 1.4 mg/m²
Patient: 80 kg, 180 cm → BSA = 1.95 m²
Dose: 50 mg/m²/day
Child: 20 kg, 110 cm → BSA = 0.80 m² (Haycock)
Dose: 4 mg/kg/BSA
Patient: 70 kg, 175 cm → BSA = 1.85 m²
For most purposes, use Mosteller—it's the simplest, most commonly used, and recommended by major medical organizations. Du Bois is acceptable and historically established. Haycock for pediatric patients.
All major formulas are accurate within ±10% for most populations. Accuracy decreases in extreme cases (very obese, very lean, very tall/short). When exact accuracy matters clinically, doctors may adjust based on other factors.
Yes. BSA directly incorporates weight, so gaining 10 pounds increases BSA, losing 10 pounds decreases it. Height is constant, so weight changes are the main factor affecting BSA over time.
Roughly 0.01-0.015 m² change per 10 lbs gained or lost, depending on height (ranges from ~0.001 to ~0.02 m² per pound depending on your current BSA and body dimensions).
Not routinely. Fitness typically uses body weight, BMI, body fat percentage, and lean body mass. However, some research uses BSA for comparing metabolic rates across individuals.
Surprisingly, sometimes yes. BSA is a function of height and weight, but very obese people often have less surface area relative to their volume than expected (due to rounded, compact shape). This is one reason BSA-based dosing can be inaccurate in severe obesity.