Predicted Body Weight Formula
Most Commonly Used Formula
The most commonly used predicted body weight (PBW) formula is the Devine formula (1974), which calculates ideal body weight as 50 kg + 2.3 kg per inch over 5 feet for men, and 45.5 kg + 2.3 kg per inch over 5 feet for women. 1
However, it's important to note that while the Devine formula is most widely used in clinical practice, the Robinson formula appears to be the best equation for calculating desirable/healthy weights in men when compared to BMI of 22 kg/m², though no formula predicted accurately for women. 2
Alternative Formulas in Clinical Use
The Devine Formula (1974)
- For men: IBW (kg) = 50 kg + 2.3 kg × (height in inches - 60) 1
- For women: IBW (kg) = 45.5 kg + 2.3 kg × (height in inches - 60) 1
- This formula is derived from Metropolitan Life Insurance Company height-weight tables and remains the most commonly referenced in clinical practice 1
Alternative Formulas from Research
- The Hamwi formula (1964): For men, IBW = 48 kg + 2.7 kg/inch over 5 feet; for women, IBW = 45.5 kg + 2.2 kg/inch over 5 feet 1
- The Robinson formula: Provides the closest approximation to BMI 22 kg/m² for men 2
- The simplified formula: IBW = 22 × H² (where H = height in meters) yields values midway within the range of published IBW formulas 3
Clinical Context and Limitations
When PBW Formulas Are Used
Predicted body weight is essential for calculating energy requirements, drug dosing, and nutritional assessments, particularly in patients with obesity or malnutrition. 4
- For energy calculations in obesity: ESPEN recommends using adjusted body weight = (actual body weight - ideal body weight) × 0.25 + ideal body weight 4
- For protein dosing in obesity: ASPEN/SCCM recommends 2.0 g/kg ideal body weight per day for BMI 30-39.9, and up to 2.5 g/kg ideal body weight per day for BMI ≥40 4
- For fluid management in obesity: Maintenance fluids should be calculated at 30-35 mL/kg/day using ideal body weight 5
Critical Limitations to Recognize
All PBW formulas show reduced accuracy at extremes of body weight and in certain populations. 4
- Most height-weight tables and formulas predict IBWs within BMI range of 20-25 kg/m², but for shorter heights formulas are closer to BMI 20 kg/m² and for taller heights closer to BMI 25 kg/m² 2
- The formulas perform poorly in severely malnourished patients (around 45% accuracy in anorexia nervosa) and in patients with obesity (around 60% accuracy at best) 4
- No formula accurately predicts ideal body weight for women when compared to BMI 22 kg/m² 2
Practical Recommendation
In clinical practice, use the Devine formula for initial calculations, but recognize that BMI ranges (20-25 kg/m²) may be more useful than IBW formulas, particularly for women. 2 For drug dosing calculations requiring precise pharmacokinetic determinations, formulas derived from actual height-weight data should be used rather than empirical methods. 1