Predicted Body Weight Formula
For clinical use, the most widely accepted ideal body weight (IBW) formulas are: IBW (kg) = height (cm) - 100 for males and IBW (kg) = height (cm) - 105 for females. 1
Standard IBW Formulas
The most commonly applied formulas in clinical practice are:
Males
- IBW (kg) = height (cm) - 100 1
- Alternative: IBW (kg) = 51.65 kg + 1.85 kg/inch of height greater than 5 feet 2
Females
- IBW (kg) = height (cm) - 105 1
- Alternative: IBW (kg) = 48.67 kg + 1.65 kg/inch of height greater than 5 feet 2
BMI-Based Alternative
A simpler universal approach uses BMI 22 as the target:
IBW (kg) = 22 × height (m)² 3, 4, 5
This formula is derived from Japanese population studies showing BMI 22.2 kg/m² in men and 21.9 kg/m² in women associated with lowest morbidity 4, 5. The value of 22 represents a practical approximation that applies across both sexes.
Clinical Application Context
When to Use Each Formula
Drug dosing calculations: Use the height-based formulas (height - 100 or 105) as these align with pharmacokinetic studies and anesthesia guidelines 1, 2
Nutritional assessment: Either approach is acceptable, though the BMI-based formula (22 × height²) provides consistency with modern obesity classification systems 3, 4
Obese patients requiring adjusted dosing: Calculate adjusted body weight (ABW) as: ABW (kg) = IBW (kg) + 0.4 × (actual weight - IBW) 1
Important Caveats
The height-based formulas (height - 100/105) are empirically derived from Metropolitan Life Insurance tables and represent population averages rather than individualized targets 2, 6. These formulas:
- Assume weight increases linearly with height, which oversimplifies body composition 6
- Do not account for frame size, muscle mass, or ethnic variations 7
- Were developed from 1885-1908 life insurance data on predominantly Caucasian populations 6
For Asian populations, lower BMI cutoffs should be considered, suggesting IBW calculations using BMI 21-22 rather than the standard formulas may be more appropriate 8.
Lean Body Weight Distinction
Lean body weight (LBW) differs from IBW and represents actual fat-free mass. The Janmahasatian formula is most widely used 1:
- Males: LBW (kg) = [9270 × actual weight (kg)] / [6680 + (216 × BMI)]
- Females: LBW (kg) = [9270 × actual weight (kg)] / [8780 + (244 × BMI)]
Note that LBW rarely exceeds 100 kg in men or 70 kg in women regardless of total body weight 1.