Ideal Body Weight Calculator — Devine Formula
Ideal Body Weight
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Formula Used
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In Kilograms
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How Ideal Body Weight Works
Ideal body weight (IBW) is an estimated weight based on height and gender that serves as a clinical reference point for medication dosing, ventilator settings, and nutritional assessment. The most widely used formula is the Devine formula, published by Dr. B.J. Devine in 1974 and adopted as the standard by the American Society of Health-System Pharmacists (ASHP) for weight-based drug dosing. According to a review published in the Annals of Pharmacotherapy, over 90% of hospital pharmacists use the Devine formula when calculating weight-based medication doses.
IBW differs from "healthy weight" in an important way: it was not designed as a personal health target but rather as a pharmacological reference. A person's actual healthy weight depends on body composition, bone density, muscle mass, and other factors that IBW does not capture. For a more comprehensive assessment, combine IBW with BMI, body fat percentage, and waist circumference measurements. The ideal weight calculator compares multiple formulas (Devine, Hamwi, Robinson, Miller) side by side for a broader perspective.
The Devine Formula
The Devine formula was originally published in 1974 for calculating gentamicin dosing and has since become the standard IBW formula in clinical practice.
- Males: IBW (kg) = 50 + 2.3 x (height in inches - 60)
- Females: IBW (kg) = 45.5 + 2.3 x (height in inches - 60)
Worked example: A 5'10" (70 inches) male: IBW = 50 + 2.3 x (70 - 60) = 50 + 23 = 73 kg (160.9 lbs). A 5'6" (66 inches) female: IBW = 45.5 + 2.3 x (66 - 60) = 45.5 + 13.8 = 59.3 kg (130.7 lbs). Both calculations assume height at or above 5 feet (60 inches).
Key Terms You Should Know
- Ideal Body Weight (IBW): A height-based weight estimate used primarily in clinical settings for drug dosing and ventilator tidal volume calculation. Not a personal fitness goal.
- Adjusted Body Weight (AdjBW): Used for obese patients: AdjBW = IBW + 0.4 x (Actual Weight - IBW). This accounts for the fact that adipose tissue has some metabolic activity. Use the adjusted body weight calculator for this calculation.
- Lean Body Mass (LBM): The total body weight minus fat mass. LBM is more relevant than IBW for drug dosing of highly lipophilic medications.
- Tidal Volume: The volume of air moved in or out of the lungs with each breath. In mechanical ventilation, tidal volume is calculated as 6-8 mL/kg of IBW (not actual weight), per guidelines from the ARDS Network.
- BMI (Body Mass Index): Weight in kg divided by height in meters squared. A BMI of 18.5-24.9 is considered healthy by the WHO. Unlike IBW, BMI uses actual weight and provides a range rather than a single target.
IBW Formula Comparison by Height
The table below compares IBW results from four established formulas. The Devine formula is most commonly used in hospital settings, while the Robinson and Miller formulas tend to produce slightly lower estimates for taller individuals.
| Height | Devine (M/F) | Hamwi (M/F) | Robinson (M/F) | Miller (M/F) |
|---|---|---|---|---|
| 5'2" (157 cm) | 54.6 / 50.1 kg | 53.4 / 49.9 kg | 55.8 / 52.4 kg | 59.0 / 55.8 kg |
| 5'6" (168 cm) | 63.8 / 59.3 kg | 64.2 / 58.7 kg | 63.4 / 59.2 kg | 64.6 / 61.3 kg |
| 5'10" (178 cm) | 73.0 / 68.5 kg | 75.0 / 67.5 kg | 71.0 / 66.0 kg | 70.3 / 66.7 kg |
| 6'2" (188 cm) | 82.2 / 77.7 kg | 85.8 / 76.3 kg | 78.6 / 72.8 kg | 75.9 / 72.1 kg |
Practical Examples
Example 1 -- Drug dosing for an obese patient: A 5'8" male weighing 120 kg needs vancomycin. His Devine IBW is 50 + 2.3 x 8 = 68.4 kg. Since his actual weight exceeds IBW by more than 30%, the pharmacist uses adjusted body weight: AdjBW = 68.4 + 0.4 x (120 - 68.4) = 68.4 + 20.6 = 89.0 kg. The dose is calculated on 89 kg rather than 120 kg, preventing potential toxicity.
Example 2 -- Ventilator tidal volume: A 5'4" female patient is placed on mechanical ventilation. Her Devine IBW = 45.5 + 2.3 x 4 = 54.7 kg. Following ARDS Network lung-protective ventilation protocols, tidal volume is set at 6-8 mL/kg IBW, yielding 328-438 mL. Using actual weight instead could lead to dangerously high tidal volumes and ventilator-induced lung injury.
Example 3 -- Nutritional assessment: A 5'11" male patient weighs 62 kg. His Devine IBW is 75.3 kg. At 82% of IBW, he may be classified as mildly malnourished (below 90% of IBW is a common threshold). The clinical dietitian uses this assessment to recommend caloric supplementation, targeting a caloric intake of 25-30 kcal/kg IBW per day (1,883-2,259 kcal).
Tips for Using Ideal Body Weight
- Do not use IBW as a personal weight goal: IBW formulas were designed for clinical calculations, not as health targets. A healthy weight range based on BMI (18.5-24.9) or body fat percentage provides a more individualized picture.
- Use adjusted body weight for obese patients: When actual weight exceeds IBW by more than 30%, most pharmacists switch to adjusted body weight for drug dosing to avoid underdosing. The 0.4 correction factor accounts for adipose tissue's partial metabolic activity.
- Understand the formula's limitations: The Devine formula was validated on adult populations of European descent and may not be equally accurate across all ethnic groups. It produces no result for heights below 5 feet and may overestimate IBW for very tall individuals.
- Compare multiple formulas: The Devine, Hamwi, Robinson, and Miller formulas can produce results varying by 5-10 kg for the same height. Using the range across formulas gives a more realistic target zone. The ideal weight calculator shows all four side by side.
- Consider body composition: Athletes and heavily muscled individuals may exceed their IBW while being perfectly healthy. A body fat measurement provides a more meaningful health indicator for such individuals.
Frequently Asked Questions
What is the Devine formula for ideal body weight?
The Devine formula calculates ideal body weight as: Males = 50 kg + 2.3 kg per inch over 5 feet; Females = 45.5 kg + 2.3 kg per inch over 5 feet. Published by Dr. B.J. Devine in 1974, it was originally developed for calculating gentamicin antibiotic doses but became the standard IBW formula in clinical pharmacy and medicine. According to the American Society of Health-System Pharmacists, it remains the most commonly referenced IBW formula for weight-based drug dosing, ventilator tidal volume calculations, and nutritional assessments across U.S. hospitals.
Is ideal body weight the same as a healthy weight?
No, IBW and healthy weight serve different purposes. IBW is a single-point clinical estimate designed for medication dosing and medical calculations -- it does not account for body composition, muscle mass, bone density, or frame size. A healthy weight, in contrast, is typically defined as a BMI between 18.5 and 24.9 (per the WHO), which provides a range rather than a single number. For a 5'10" male, the Devine IBW is 73 kg (161 lbs), while the healthy BMI range spans 58.5-79 kg (129-174 lbs). Athletes with high muscle mass may exceed their IBW while being in excellent health.
What if I am shorter than 5 feet?
The Devine formula was validated for adults 5 feet (60 inches) and taller. For shorter individuals, the formula produces zero or negative values and should not be used. Alternative approaches for patients under 5 feet include using actual body weight with clinical adjustment, the Broca Index (weight in kg = height in cm - 100), or BMI-based ranges. Pediatric patients use age-specific growth charts from the CDC rather than adult IBW formulas. Some clinicians use the Hamwi formula with modifications for shorter stature, though no widely accepted standard exists.
How is ideal body weight used in mechanical ventilation?
In mechanical ventilation, tidal volume (the amount of air delivered per breath) is calculated based on IBW, not actual weight. The ARDS Network's landmark study demonstrated that using 6-8 mL/kg of IBW significantly reduced mortality in acute respiratory distress syndrome patients compared to higher volumes. For a 5'6" female patient (IBW 59.3 kg), the target tidal volume would be 356-474 mL. Using actual weight in an obese patient could result in dangerously high tidal volumes that cause ventilator-induced lung injury, making accurate IBW calculation a critical patient safety measure.
What is the difference between IBW and adjusted body weight?
Adjusted body weight (AdjBW) is a modification of IBW used for patients whose actual weight significantly exceeds their ideal weight (typically by more than 30%). The formula is AdjBW = IBW + 0.4 x (Actual Weight - IBW). The 0.4 correction factor accounts for the fact that adipose tissue has some metabolic activity, meaning drugs distribute partially into fat. For example, a 5'8" male (IBW 68.4 kg) weighing 120 kg would have an AdjBW of 89.0 kg. Dosing on actual weight (120 kg) risks overdosing, while dosing on IBW alone (68.4 kg) may underdose. AdjBW provides the middle ground.