Devine Formula (Ideal Body Weight)
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Variables
| Symbol | Name | Unit | Description |
|---|---|---|---|
| $IBW$ | Ideal Body Weight | kg | Estimated ideal body weight for a given height. |
| $h_in$ | Height | inches | Standing height in inches above 5 feet (60 inches). |
What Is the Devine Formula?
The Devine formula estimates Ideal Body Weight (IBW) for adults based on height. The male formula is:
$$IBW_{male} = 50 + 2.3 \times (h_{in} - 60)$$
$$IBW_{female} = 45.5 + 2.3 \times (h_{in} - 60)$$
Here, h_in is height in inches, and 60 inches (5 feet) is the baseline height. For every inch above 5 feet, 2.3 kg is added to the base weight.
Primary Clinical Use: Drug Dosing
IBW is not primarily a weight-loss target — it is used in pharmacokinetics to calculate drug doses. Many medications (aminoglycosides, anaesthetic agents, tidal volumes in ventilated patients) are dosed on IBW rather than actual body weight, because these drugs distribute into lean tissue, not fat. Dosing on actual weight in obese patients can cause toxicity; dosing on IBW in very thin patients may undertreat.
Why 2.3 kg Per Inch?
The 2.3 kg/inch increment was derived empirically from life-insurance actuarial tables that related height to the body weight associated with lowest mortality in the mid-20th century. It is not based on body composition science but on population survival statistics.
Limitations
The Devine formula was published in 1974 before modern body composition analysis. It: - Does not adjust for age or sex hormonal status - Produces fixed IBW regardless of frame size (bone density, musculature) - Is not validated for children or elderly populations - Often yields values that BMI guidelines would classify as low-normal
It should not be used as a personal weight-loss goal without medical guidance.
Derivation & History
B.J. Devine published the formula in 1974 in a pharmacology paper on gentamicin dosing. The goal was to estimate the lean body mass (LBM) of patients in order to calculate appropriate antibiotic doses. Devine selected the base weights (50 kg male, 45.5 kg female at 5 feet) and the 2.3 kg/inch increment from actuarial life-insurance data tables that associated specific height-weight combinations with lowest long-term mortality.
The formula was never intended as a fitness or obesity tool; it was a pharmacokinetic convenience tool. Its widespread use in weight-management contexts is a case of clinical scope creep. Later investigators (e.g., Miller in 1983, Robinson in 1983) proposed alternative IBW equations, but Devine remains dominant in clinical pharmacokinetics.
Worked Examples
Male, 5 ft 10 in tall
- Inches above 5 ft: 70 − 60 = 10 inches
- IBW = 50 + 2.3 × 10 = 50 + 23 = 73 kg
Result: IBW = 73 kg
Female, 5 ft 4 in tall
- Inches above 5 ft: 64 − 60 = 4 inches
- IBW = 45.5 + 2.3 × 4 = 45.5 + 9.2 = 54.7 kg
Result: IBW = 54.7 kg
Edge Cases & Limitations
Height below 5 feet: The formula extrapolates negatively and is not validated below 60 inches; clinical pharmacists use alternative equations or actual body weight in very short patients.
Morbid obesity: For patients with BMI ≥ 40, adjusted body weight (ABW = IBW + 0.4 × (actual − IBW)) is used for some drug calculations.
Paediatric patients: Devine is not validated for children; weight-for-age charts and body surface area are used instead.
Very muscular individuals: May have actual body weight substantially above IBW, yet be metabolically healthy — the formula would incorrectly suggest they are overweight.
Real-World Applications
Hospital pharmacists use IBW daily for aminoglycoside (gentamicin, tobramycin) dosing, heparin infusion rates, and anaesthetic agent calculation. Respiratory therapists set ventilator tidal volumes (6 mL/kg IBW) to prevent barotrauma in ICU patients. Nephrologists use IBW to adjust dialysis clearance targets. These applications occur thousands of times daily in hospitals worldwide, making Devine's 1974 formula one of the most clinically impactful equations in modern medicine.