Medical AIDevine ideal and adjusted body weight calculator
The Devine formula estimates ideal body weight from sex and height, the basis many drugs use for weight-based dosing instead of actual weight. Adjusted body weight blends ideal and actual weight (correction factor 0.4) for drugs that partly distribute into excess tissue.
How to measure each input
- Height
- Use measured standing height. The formula is built around inches over 60 (5 feet), so the centimetre value is converted using 1 inch = 2.54 cm before applying the 2.3 kg per inch increment.
- Sex base weight
- Men start from 50 kg and women from 45.5 kg at a height of 60 inches, then add 2.3 kg for each additional inch.
- Adjusted body weight
- Enter actual weight to apply IBW + 0.4 x (actual - IBW). The 0.4 correction factor reflects that excess tissue contributes partially to the distribution of some drugs. It is only used when actual weight exceeds ideal.
Interpretation
| Band | Meaning |
|---|---|
| Below the validated range | A non-positive ideal body weight means the entered height is below 5 feet (60 inches), where the Devine formula extrapolates below its intended range. Interpret with caution and use clinical judgement or a height-specific method. |
| Estimated ideal body weight | This is the Devine ideal body weight for the entered sex and height. Whether to dose a given drug on ideal, adjusted, or actual weight is drug-specific: follow the medication's labelling or local dosing guideline. |
Pitfalls, exclusions and caveats
- The Devine equation is an empirical formula that originated for drug dosing (gentamicin), not a measurement of true lean mass. Treat it as a dosing convention, not a physiological gold standard.
- It is not designed for heights under 5 feet (60 inches): below that the formula extrapolates and can return implausibly low or negative weights.
- The choice between ideal, adjusted, and actual body weight is drug-specific. Using the wrong basis can under- or over-dose. Always check the drug's labelling or a dosing reference.
- The 0.4 adjustment factor is a widely used convention; some agents or guidelines use a different factor (for example 0.3) or specify total body weight, so confirm per drug.
IBW (kg) = base + 2.3 x (height in inches - 60), where base is 50 for men and 45.5 for women; height(inches) = height(cm) / 2.54. Adjusted body weight = IBW + 0.4 x (actual weight - IBW), applied when actual weight exceeds IBW.The ideal body weight equation is attributed to Devine (1974) and its history is reviewed by Pai and Paloucek (2000). This implementation is an educational tool and is not affiliated with the original authors.
Frequently asked
When should I use ideal versus adjusted versus actual body weight?
It depends on the drug. Some medications dose on ideal body weight, some on adjusted body weight in obesity, and others on actual (total) body weight. There is no universal rule, so check the specific drug's dosing guidance rather than defaulting to one weight.
Where does the 0.4 correction factor in adjusted body weight come from?
Adjusted body weight = IBW + 0.4 x (actual - IBW). The 0.4 reflects the idea that roughly 40% of the excess weight above ideal contributes to the distribution volume of many drugs. It is a dosing convention, and some references use a different factor.
Why does the formula behave oddly for short patients?
The Devine formula is anchored at 60 inches (5 feet) and subtracts 2.3 kg per inch below that. For heights well under 5 feet it extrapolates beyond its intended range and can produce very low or negative weights, so use clinical judgement there.
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