What is the formula to calculate body surface area (BSA)?

Calculating Body Surface Area (BSA)

The most widely used and recommended formula for calculating body surface area (BSA) is the Mosteller formula: BSA (m²) = √[(Height(cm) × Weight(kg))/3600].

Common BSA Formulas

Mosteller Formula (Recommended)

• Formula: BSA (m²) = √[(Height(cm) × Weight(kg))/3600]
• Advantages: Simple to calculate, easily remembered, and can be evaluated on a pocket calculator 1
• Validation: Extensively validated and shows excellent correlation with other formulas

DuBois and DuBois Formula

• Formula: BSA (m²) = 0.007184 × Height(cm)^0.725 × Weight(kg)^0.425
• Limitations: Derived from only 9 subjects but still widely used 1
• Note: May underestimate BSA in obese patients by 3-5% 1

Gehan and George Formula

• Formula: BSA (m²) = 0.0235 × Height(cm)^0.42246 × Weight(kg)^0.51456
• Advantages: Based on a larger sample of 401 surface area measurements 2
• Note: This formula is particularly useful in pediatric settings 3

Simplified Formula

• Formula: BSA (m²) = 1/6 × √(Weight(kg) × Height(m))
• Advantages: Uses SI units and provides a rational approach 4

Clinical Applications of BSA

BSA calculations are critical in multiple clinical scenarios:

1. Medication Dosing:

   • Particularly important for chemotherapeutic agents with narrow therapeutic indices
   • Helps adjust medication doses for patients with renal insufficiency 3

2. Cardiac Function Assessment:

   • Used to index cardiac output and other hemodynamic parameters
   • Critical in valvular heart disease management 3

3. Renal Function Evaluation:

   • GFR is typically normalized to 1.73 m² BSA
   • Essential for staging chronic kidney disease 3

4. Valvular Heart Disease Management:

   • Left ventricular size parameters are often indexed to BSA
   • Critical for timing surgical interventions in conditions like aortic regurgitation 3

Special Considerations

Pediatric Patients

• For children, the Gehan and George equation is recommended as it was derived from the greatest number of subjects 3
• A simplified weight-based formula for children: BSA (m²) = [4W(kg)+7]/[90+W(kg)] shows excellent correlation with the Mosteller formula 5

Obese Patients

• Traditional formulas may underestimate BSA in obese patients
• The DuBois formula underestimates BSA in obese patients by 3% (male) to 5% (female) 1

Elderly and Small-Stature Patients

• Women and patients with smaller stature may require special attention when BSA calculations are used for clinical decision-making 3
• Late surgical results for conditions like aortic regurgitation can be less satisfactory in women because standard left ventricular size parameters are applied without proper BSA normalization 3

Practical Approach

1. For routine clinical use: Use the Mosteller formula for its simplicity and accuracy
2. For research purposes: Consider using the Gehan and George formula due to its statistical robustness
3. For pediatric patients: Either the Mosteller formula or the pediatric-specific weight-based formula is appropriate
4. For obese patients: Be aware that traditional formulas may slightly underestimate BSA

The Mosteller formula provides the best balance of accuracy and simplicity for most clinical applications, making it the preferred method for calculating BSA in everyday practice.