Skip to content
Rapid VentRapid Vent Calculator

Devine formula: calculating ideal body weight for adult ventilation

Published 

The Devine formula estimates ideal body weight from height and sex: 50 kg for men and 45.5 kg for women, plus 2.3 kg for every inch over 5 feet. For the mechanically ventilated adult, that ideal body weight, not the number on the stretcher report, is what tidal volume gets sized from. Adult patients only: every result is a starting-point estimate, checked against the patient and your local protocol.

  • Male: IBW (kg) = 50 + 2.3 x (height in inches − 60)
  • Female: IBW (kg) = 45.5 + 2.3 x (height in inches − 60)

The Devine formula for men and women, in inches and centimeters

Both sexes share the same shape: a baseline weight plus 2.3 kg per inch above 5 feet. Men run 50 kg plus 2.3 kg per inch over 60 inches; women run 45.5 kg plus 2.3 kg per inch over 60 inches. The centimeter version comes from the ARDSNet predicted body weight (PBW) equation, as reproduced by Wilson and Matthay (2014): 50 or 45.5 kg plus 0.91 kg per centimeter over 152.4 cm. The two forms differ by a fraction of a kilogram. Rapid Vent’s own choice is to round centimeters to the nearest whole inch and run the inch form instead of the 0.91 coefficient.

How to calculate IBW for a ventilator: two worked examples

Two examples show the arithmetic end to end.

A 5-foot-9 woman. Height is 69 inches: 45.5 + 2.3 x (69 - 60) = 45.5 + 20.7 = 66.2 kg, not her weight on the stretcher.

A 183 cm man. Rapid Vent rounds 183 cm to the nearest whole inch first, 72, then runs 50 + 2.3 x (72 - 60) = 50 + 27.6 = 77.6 kg.

Ideal body weight is where this calculation stops. Tidal volume and rate come next, in adult ventilator settings, step by step.

Where the Devine formula came from: a 1974 drug-dosing case

The Devine formula started nowhere near a ventilator. Devine BJ published it in 1974 (Drug Intell Clin Pharm 1974;8:650-655), a case report on adjusting a gentamicin dose, cited here through Pai and Paloucek’s 2000 review rather than from the original, which sits behind a publisher paywall. Pai and Paloucek describe how it caught on: the pharmacokinetics of certain drugs correlated with ideal body weight, and Devine’s equations matched an older height-weight-table rule already in use. Their conclusion was blunt: any of that era’s equations could estimate it. Devine’s was a drug-dosing equation; IBW became ventilation’s number later, borrowed for a different reason.

Why adult ventilator settings use ideal body weight, not actual weight

Lungs scale with height and sex, not scale weight. The ARMA trial sized every breath from a predicted body weight (PBW) calculated from height and sex. Its methods cite a drug-data handbook for that equation, not Devine directly, but the arithmetic matches: the ARDSNet PBW equation and the Devine IBW equation are arithmetically identical.

The split matters on the other side of the chart too. Tidal volume here and in the app runs on ideal body weight. Rapid Vent’s own RSI medication doses run on actual body weight instead, and for some RSI drugs in obesity, references differ on the right basis; this page doesn’t pick a side, and the actual-weight basis for RSI medication doses covers the split.

Turning ideal body weight into a breath size is the tidal volume calculator for adult ventilator settings, and the ARDSnet protocol settings that start from predicted body weight build the rest of the card from there.

Devine IBW by height, 5 feet to 7 feet

The same formula, run across the adult height range, reads as a table below. It starts at 60 inches, the shortest height the formula covers, and stops at Rapid Vent’s own upper height gate, 84 inches (213 cm). Tidal volume at 4, 6, and 8 mL/kg, from 5 feet to 6 feet 6 inches, is charted on the tidal volume calculator page.

Devine formula ideal body weight by height (adults, 60 to 84 inches)
Height (ft/in)Height (in)cmIBW male (kg)IBW female (kg)
5′0″60152.450.045.5
5′3″63160.056.952.4
5′6″66167.663.859.3
5′9″69175.370.766.2
6′0″72182.977.673.1
6′3″75190.584.580.0
6′6″78198.191.486.9
6′9″81205.798.393.8
7′0″84213105.2100.7

Inch-form Devine output; the cm column is a conversion of the inch value (the 84-inch row shows Rapid Vent’s 213 cm ceiling), not the output of the 0.91 cm form. The table starts at 60 inches because the formula is formally defined only above about 5 feet (Martin and Richards, 2017).

Verify the edge cases: under 5 feet, very tall, and obesity

Three groups need a second look: patients under 5 feet, patients at the very tall end, and patients with obesity.

Devine formula ideal body weight by height, men and womenTwo lines from 60 to 84 inches. Men start at 50.0 kg and women at 45.5 kg; both add 2.3 kg per inch, so the 4.5 kg gap between sexes holds constant at every height.MenWomen406080100110kg60 in66 in72 in78 in84 inFormula defined from about 5 ftRapid Vent upper height gateM 50.0M 105.2F 45.5F 100.7
The 4.5 kg gap between the sexes’ baselines stays constant across the height range; both lines rise at the same 2.3 kg per inch.

Under 5 feet (60 inches)

Martin and Richards’ 2017 analysis notes that the formula is formally defined only above about 5 feet, so no raw Devine number for a shorter height prints here. Rapid Vent’s own choice holds ideal body weight at the 50 or 45.5 kg baseline at or below 60 inches, and refuses entries under 58 inches: both are implementation choices, not clinical guidance. Pediatric patients are out of scope.

Very tall patients

The formula is linear, climbing 2.3 kg per inch with no ceiling. Rapid Vent’s app refuses any height above 84 inches (213 cm) and asks the user to verify the entry. Martin and Richards note, in a theoretical model, that established predicted-body-weight formulas increasingly over-estimate lean body weight in taller patients.

Obesity: actual weight versus ideal body weight

Ideal body weight does not move with body weight, and for tidal volume that’s the point. Martin and Richards summarize the rationale: a tidal volume based on actual body weight might lead to volutrauma in a patient with obesity, or inadequate ventilation in an underweight one. That’s the same actual-versus-ideal split covered above.

Compare the Devine formula with Robinson, Miller, and Hamwi

Devine’s wasn’t the only ideal-body-weight equation. Hamwi published one in 1964; Robinson and Miller followed in 1983, both built for drug dosing, as Peterson and colleagues’ 2016 comparison lists them. Walter and Patel found spreads between Devine and other formulas running up to 14% in men and 19% in women. Pai and Paloucek’s answer: any of them can estimate ideal body weight, because the underlying height-weight tables largely agree. For adult ventilation the fact that matters is narrower than a ranking: the equation in the ARDSNet protocol runs the same arithmetic as the Devine formula, so ventilation references keep landing on his numbers.

Is IBW still used today?

Yes, in two places. Ventilation references still run the ARDSNet PBW equation, arithmetically the Devine formula, to size a protective breath. Pharmacy references still use Devine’s equations for drug dosing and, per Erstad, for creatinine clearance. The next step in this chain turns that kilogram into the minute ventilation target built on IBW, and every number downstream still has to fit the patient and protocol in front of you.

Sources

  1. Pai MP, Paloucek FP. The origin of the “ideal” body weight equations. The Annals of Pharmacotherapy. 2000;34(9):1066-1069. https://pubmed.ncbi.nlm.nih.gov/10981254/
  2. Erstad BL. Predicted body weight: A rose by any other name. American Journal of Health-System Pharmacy. 2021;78(8):751-753. https://academic.oup.com/ajhp/article-abstract/78/8/751/6134318
  3. Martin DC, Richards GN. Predicted body weight relationships for protective ventilation: unisex proposals from pre-term through to adult. BMC Pulmonary Medicine. 2017;17:85. https://pmc.ncbi.nlm.nih.gov/articles/PMC5442651/
  4. The Acute Respiratory Distress Syndrome Network (Brower RG, et al). Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome. New England Journal of Medicine. 2000;342(18):1301-1308. https://pubmed.ncbi.nlm.nih.gov/10793162/
  5. Wilson JG, Matthay MA. Mechanical ventilation in acute hypoxemic respiratory failure: a review of new strategies for the practicing hospitalist. Journal of Hospital Medicine. 2014;9(7):469-475. https://pmc.ncbi.nlm.nih.gov/articles/PMC4139286/
  6. Walter E, Patel A. Variability in ideal body weight formulae. Journal of the Intensive Care Society. 2023;24(3 Suppl):16-17. https://pmc.ncbi.nlm.nih.gov/articles/PMC10621523/
  7. Peterson CM, Thomas DM, Blackburn GL, Heymsfield SB. Universal equation for estimating ideal body weight and body weight at any BMI. American Journal of Clinical Nutrition. 2016;103(5):1197-1203. https://pmc.ncbi.nlm.nih.gov/articles/PMC4841935/