About the Tidal Volume Calculator
Lung-protective ventilation sizes the tidal volume to the patient’s predicted body weight (PBW) — which depends only on sex and height — rather than actual weight, because lung size tracks height. This calculator uses the ARDS Network formulas (men: 50 + 2.3 × (height in inches − 60); women: 45.5 + 2.3 × (height in inches − 60)) and multiplies PBW by your chosen mL/kg target.
In the landmark ARDSNet trial (NEJM 2000), ventilating patients with acute lung injury and ARDS at an initial 6 mL/kg PBW with a plateau pressure of 30 cmH₂O or less cut mortality from 39.8% to 31.0% compared with 12 mL/kg. The ARDSNet protocol starts at 8 mL/kg and reduces to 6 mL/kg, allowing 4–8 mL/kg depending on plateau pressure, pH and patient comfort. The table shows the volume at every step from 4 to 8 mL/kg.
It is designed for ICU clinicians, respiratory therapists, anaesthetists and trainees. The formula was used in adults; it is not valid for children or for adults shorter than about 152 cm (60 in), where the result falls below the formula’s base weight. Ventilator settings must always be adjusted to measured plateau pressure, gas exchange and the clinical situation.
With the default inputs, the tidal volume at target is 423 mL. Change any value above to recalculate instantly.
How to use the tidal volume calculator
- 1Select the patient’s sex.
- 2Choose centimetres or inches and enter the measured height.
- 3Pick the target tidal volume in mL/kg (6 mL/kg is the usual lung-protective goal).
- 4Read the predicted body weight and tidal volume.
- 5Use the 4–8 mL/kg table when adjusting to plateau pressure.
Formula and method
Predicted body weight is calculated with the ARDS Network formulas, which add 2.3 kg for every inch of height above 5 feet (60 inches) to a base of 50 kg for men and 45.5 kg for women. Heights in centimetres are converted with 1 in = 2.54 cm (the equivalent metric form is about 0.91 × (cm − 152.4)).
The tidal volume is PBW multiplied by the chosen mL/kg. The ARDSNet protocol sets an initial tidal volume of 8 mL/kg and reduces it by 1 mL/kg at intervals of 2 hours or less until 6 mL/kg is reached, then adjusts between 4 and 8 mL/kg to keep plateau pressure at or below 30 cmH₂O and pH in the target range.
- PBW
- Predicted body weight, kg
- VT
- Tidal volume, mL
Worked examples
Man, 175 cm, 6 mL/kg
175 cm is 68.9 in. PBW = 50 + 2.3 × 8.9 = 70.5 kg, so 6 mL/kg gives about 423 mL.
Woman, 5 ft 4 in, starting at 8 mL/kg
PBW = 45.5 + 2.3 × 4 = 54.7 kg. The initial ARDSNet tidal volume of 8 mL/kg is 438 mL, which would then be reduced towards 6 mL/kg (328 mL).
Tall man, 190 cm, 4 mL/kg
190 cm is 74.8 in, giving PBW = 50 + 2.3 × 14.8 = 84.0 kg. At 4 mL/kg the tidal volume is about 336 mL.
Frequently asked questions
Why use predicted rather than actual body weight?+
Lung volume is determined mainly by height and sex, not by body fat. Using actual weight in an obese patient would give a dangerously large tidal volume, so lung-protective ventilation uses predicted body weight.
What is a lung-protective tidal volume?+
For ARDS, about 6 mL/kg of predicted body weight with a plateau pressure of 30 cmH₂O or less, based on the ARDSNet trial. Many clinicians also use 6–8 mL/kg PBW for ventilated patients without ARDS.
Is predicted body weight the same as ideal body weight?+
The ARDSNet predicted body weight formula is essentially the Devine ideal body weight formula (50 or 45.5 kg plus 2.3 kg per inch over 5 feet). The terms are often used interchangeably in ventilation.
What did the ARDSNet trial show?+
In 861 patients with acute lung injury or ARDS, an initial tidal volume of 6 mL/kg PBW reduced mortality to 31.0% from 39.8% with 12 mL/kg, and increased ventilator-free days.
Can I use this for children?+
No. The ARDSNet PBW formula was derived for adults. Paediatric ventilation uses different weight estimates and tidal volume targets, set by paediatric intensive care teams.
For healthcare professionals and education only. This calculator implements a published formula or score but is not a diagnosis and does not replace clinical judgment. Verify inputs and results against the original source before using them in patient care.