The ideal body weight calculator uses the Devine formula to estimate a patient's IBW based on height and sex. IBW is used instead of actual body weight for drug dosing in many clinical situations — particularly aminoglycoside antibiotics (gentamicin, tobramycin), initial ventilator tidal volume settings, and nutritional calculations. When a patient's actual weight exceeds 130% of their IBW, Adjusted Body Weight (ABW) is calculated to account for the increased drug distribution in obese patients.
Use IBW for: initial ventilator tidal volume settings, aminoglycoside dosing (gentamicin, tobramycin), most general drug dosing references.
Use ABW for: patients who are obese (actual weight more than 130% of IBW), some chemotherapy regimens, and weight-based heparin in obese patients.
Use Actual Body Weight for: patients at or below their IBW, hydrophilic drugs, and paediatric dosing.
The Devine formula starts at 50 kg for men and 45.5 kg for women at 5 feet (152.4 cm), then adds 2.3 kg for every inch above that. Values rounded to one decimal place.
| Height | Male IBW | Female IBW |
|---|---|---|
| 5'0" (152 cm) | 50.0 kg | 45.5 kg |
| 5'2" (157 cm) | 54.6 kg | 50.1 kg |
| 5'4" (163 cm) | 59.2 kg | 54.7 kg |
| 5'6" (168 cm) | 63.8 kg | 59.3 kg |
| 5'8" (173 cm) | 68.4 kg | 63.9 kg |
| 5'10" (178 cm) | 73.0 kg | 68.5 kg |
| 6'0" (183 cm) | 77.6 kg | 73.1 kg |
| 6'2" (188 cm) | 82.2 kg | 77.7 kg |
A point that trips people up: ideal body weight is not a health target and was never meant to be one. It's a dosing and ventilator tool. Nobody should be told to weigh their IBW — it exists so that drugs distributed mainly in lean tissue get dosed sensibly, and so that tidal volumes are set to the size of the lungs rather than the size of the patient.
Three situations account for most of its use at the bedside. Ventilator settings come first — lung-protective tidal volumes of 6–8 mL/kg are calculated on IBW, never actual weight, because lung size tracks height rather than body mass. Drug dosing is the second: aminoglycosides and several other drugs distribute mostly in lean tissue, so actual weight would overdose an obese patient. And renal calculations are the third, where an adjusted body weight is often preferred for estimating clearance in obesity.
Where actual weight exceeds IBW substantially, many protocols use an adjusted body weight — typically IBW plus 40% of the difference between actual and ideal — as a middle ground. Which one applies is drug-specific and protocol-specific, so check your local reference rather than assuming.
Use IBW for aminoglycosides, initial ventilator tidal volumes, and as a starting point for nutritional calculations. Use Adjusted Body Weight (ABW) when the patient is obese (actual weight >130% of IBW). Use actual body weight when the patient weighs less than their IBW.
For males: IBW (kg) = 50 + 2.3 × (height in inches − 60). For females: IBW (kg) = 45.5 + 2.3 × (height in inches − 60). The formula requires height above 5 feet (60 inches / 152 cm) to be valid.
About 68.4 kg using Devine. It starts at 50 kg for a man at 5 feet and adds 2.3 kg per inch, so eight inches adds 18.4 kg.
No. IBW is a dosing and ventilator tool, not a health or weight-loss target. It exists so drugs distributed in lean tissue are dosed sensibly and tidal volumes match lung size. A healthy weight range for you is a separate question for a clinician.