General
Ideal Body Weight (Devine)
Ideal body weight from height and sex.
Education and reference only. Not a substitute for clinical judgement, local policy or product labelling. Always verify before clinical use. Values are calculated in your browser and never stored.
Background
Ideal body weight (IBW) using the Devine formula estimates a reference weight from a person's height and sex, independent of their actual weight. It was originally devised to standardise drug dosing and remains widely used for weight-based calculations where actual weight may mislead — most notably setting lung-protective tidal volumes in mechanical ventilation. The formula uses a baseline value plus an increment for each inch of height above five feet, differing between men and women. The result is reported in kilograms.
Interpreting the result
The IBW reflects a height-derived target weight rather than a measured or healthy weight for an individual. It is used as the input for certain calculations — for example, tidal volume per kilogram of ideal body weight — where using actual weight would be inappropriate. In people who are markedly underweight, actual body weight may be more appropriate than IBW, and in some contexts an adjusted body weight is used instead. It is a calculation aid, not a clinical weight target for patients.
Worked example
For a man 175 cm tall (about 5 feet 9 inches), the Devine formula gives an ideal body weight of roughly 70 kg. This figure would then be used, for instance, to set a lung-protective tidal volume in ventilation rather than his measured weight.
Pearls / pitfalls
- IBW depends only on height and sex; it does not reflect actual body composition or a healthy weight goal.
- For lung-protective ventilation, tidal volume is set by ideal (predicted) body weight, not measured weight — using actual weight risks harmful over-inflation in shorter patients.
- In underweight individuals, actual weight may be lower than IBW and more appropriate for some calculations.
- Several drugs use actual, ideal or adjusted body weight depending on the agent — always check the specific dosing guidance.
Evidence & validation
The formula was published by Devine in the context of aminoglycoside dosing and, despite limited original validation, became a de facto standard. Its most important modern endorsement is in ARDS ventilation, where landmark trials set tidal volumes by predicted (ideal) body weight.
Frequently asked questions
What is ideal body weight used for?
It standardises weight-based calculations where actual weight may mislead, such as setting lung-protective tidal volumes in ventilation and certain medication calculations. It is a reference value, not a personal weight target.
Is ideal body weight the same as a healthy weight?
No. IBW is a height- and sex-derived reference figure for calculations, whereas a healthy weight is assessed clinically using measures such as body mass index alongside the individual's circumstances.
Why is it used in ventilation?
Lung size correlates with height rather than actual weight, so tidal volumes are set per kilogram of ideal body weight to deliver lung-protective ventilation and avoid over-distension, particularly in shorter patients.
Does it work at extremes of height?
The formula is least reliable at very short or very tall heights and below five feet, where the linear increment becomes inaccurate. Clinical judgement is needed at the extremes.
What about obese patients?
For some calculations an adjusted body weight, derived from ideal and actual weight, is used in obesity. The appropriate weight depends on the specific drug or calculation and its guidance.
References
- Devine BJ. Gentamicin therapy. Drug Intell Clin Pharm. 1974;8(11):650–655.
- The Acute Respiratory Distress Syndrome Network. Ventilation with lower tidal volumes for acute lung injury and the acute respiratory distress syndrome. N Engl J Med. 2000;342(18):1301–1308.
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