How Ideal Body Weight is calculated
Several regression formulas estimate a reference ("ideal") body weight from height and sex. This calculator reports all four alongside the Devine formula, which is the de facto clinical standard.
All formulas assume a "baseline" weight at 5 ft (60 in) and add a fixed increment per inch above that. Height under 5 ft is floored to 0 extra inches.
Normal values & use
There's no single "correct" IBW — the four formulas typically agree within a few kilograms. Devine is preferred in the ICU/pharmacy setting because it underpins the two most common bedside applications below.
Clinical use
- Drug dosing: aminoglycosides, and several other weight-based drugs, are dosed on IBW (or an adjusted body weight in obesity) rather than actual body weight, since drug distribution doesn't scale with excess fat mass.
- Lung-protective ventilation: ARDSNet tidal volume targets (4–8 mL/kg, typically starting at 6 mL/kg) are calculated from Devine IBW, not actual weight — using actual weight in an obese patient would over-distend the lungs.
- Obese patients: for markedly obese patients, many protocols use an Adjusted Body Weight = IBW + 0.4 × (actual weight − IBW) instead of IBW alone.
Frequently asked questions
What is ideal body weight (IBW)?
IBW is a reference weight estimated from height and sex, used mainly for weight-based drug dosing and lung-protective ventilation calculations — not as a personal weight-loss target.
Why are there different IBW formulas (Devine, Robinson, Miller, Hamwi)?
Each was derived from a different population/dataset in the mid-20th century. They typically agree within a few kilograms of each other; Devine became the de facto clinical standard because it underpins the two most common bedside uses — drug dosing and ARDSNet ventilation.
Is IBW the same as a "healthy weight"?
Not exactly — IBW is a dosing/ventilation reference point, while a healthy weight range is usually expressed through BMI. They often overlap but serve different clinical purposes.
When is IBW used instead of actual body weight?
For weight-based drug dosing (especially in obese patients, where actual weight would overestimate distribution volume) and for calculating lung-protective tidal volumes, where actual weight would risk over-distending the lungs.
References
- Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8:650–655.
- Robinson JD, et al. Determination of ideal body weight for drug dosage calculations. Am J Hosp Pharm. 1983;40:1016–1019.
- The Acute Respiratory Distress Syndrome Network (ARDSNet). Ventilation with lower tidal volumes for ARDS. N Engl J Med. 2000;342:1301–1308.