About tidal volume and predicted body weight
Tidal volume is the amount of air moved in a single breath, whether spontaneous or delivered by a mechanical ventilator. For mechanical ventilation, tidal volume is set relative to predicted body weight (PBW) rather than a patient's actual body weight, because lung size tracks height and sex much more closely than it tracks measured weight. This calculator finds PBW with the Devine formula, then converts it to a tidal volume in milliliters and a minute ventilation in liters per minute.
The Devine formula for predicted body weight
- Male: PBW (kg) = 50 + 2.3 x (height in inches - 60)
- Female: PBW (kg) = 45.5 + 2.3 x (height in inches - 60)
- Height entered in centimeters is converted to inches internally (1 inch = 2.54 cm) before applying the formula.
From predicted body weight to tidal volume
Once PBW is known, tidal volume in milliliters is simply PBW multiplied by a target in milliliters per kilogram: Tidal volume = PBW x mL/kg. Lung-protective ventilation, as defined by the ARDSnet protocol, targets roughly 6 mL/kg PBW, with a working range of about 4 to 8 mL/kg used to keep plateau pressure at or below 30 cmH2O. Minute ventilation is tidal volume multiplied by respiratory rate, converted to liters: Minute ventilation (L/min) = (tidal volume in mL x breaths/min) / 1000.
Putting the result in context
The 4-8 mL/kg PBW band shown by this calculator is a general reference range from the lung-protective ventilation literature, not a fixed prescription. Actual ventilator settings also depend on plateau pressure, oxygenation, underlying lung disease, and the patient's clinical trajectory.
When to consult a professional
This calculator performs the standard PBW and tidal volume arithmetic for reference and education. It is not a substitute for clinical judgment. Ventilator settings for an actual patient must be determined and adjusted by a qualified healthcare provider.