Lung-protective ventilation doses tidal volume against ideal body weight rather than actual weight, because lung size scales with height and sex, not with adiposity. This article explains why the ARDSNet 6 mL/kg approach became the standard and how the Devine formula behind it works.
How the calculator works
The calculator first estimates ideal body weight (IBW) using the Devine formula: a base constant (50 kg for men, 45.5 kg for women) plus 2.3 kg for every inch of height above 60 in (5 ft). It then multiplies IBW by your chosen target — 4 to 8 mL/kg, with 6 mL/kg as the ARDSNet-recommended starting point — to get tidal volume in milliliters. Both steps run instantly as you adjust height, sex, or target.
Why ideal body weight, not actual weight
Two patients of the same height can differ in actual body weight by dozens of kilograms depending on adiposity, edema, or muscle mass, yet their lungs are roughly the same size. Dosing tidal volume from actual weight would deliver a dangerously large volume to a heavier patient with normal-sized lungs. The landmark 2000 ARDSNet trial in the New England Journal of Medicine found that capping tidal volume at 6 mL/kg IBW — instead of the older 12 mL/kg approach — reduced mortality in acute respiratory distress syndrome, and the practice has since become standard for most mechanically ventilated patients, not only those with ARDS.
Limits and edge cases
This calculator estimates a starting tidal volume target — it does not replace plateau pressure monitoring, arterial blood gas review, or an institution's ventilator protocol. The Devine formula was derived for adults; it is not intended for pediatric patients, and it was validated primarily in adults roughly 60 in and taller, which is why this calculator holds the height term at zero rather than extrapolating below that point. Actual ventilator settings must always be ordered and adjusted by a qualified clinician based on the full clinical picture.