Tidal Volume Calculator
Enter the patient's height and sex to get the ideal body weight (IBW) and the recommended tidal volume range for mechanical ventilation under the ARDSNet lung-protective protocol (4 to 8 mL/kg IBW). You can also choose a target mL/kg setting to see the exact set volume and review the spontaneous breathing reference values side by side. All calculations update in real time.
What is tidal volume?
Tidal volume (TV or VT) is the amount of air moved into or out of the lungs with each normal breath. In a healthy resting adult it averages about 500 mL, or roughly 7 mL per kilogram of ideal body weight. The term "tidal" reflects the rhythmic flow of air, much like the rise and fall of tides. Of each breath, only about 350 mL reaches the alveoli where gas exchange happens; the remaining 150 mL fills the anatomical dead space of the conducting airways and does not participate in gas exchange. Tidal volume is measured during spirometry while the patient breathes quietly, and it is one of the key variables set by a clinician when a patient requires mechanical ventilation.
Why ideal body weight (not actual weight) drives ventilator settings
Lung size correlates with height and skeletal frame, not with total body mass. An obese patient has the same lung volume as a lean person of the same height, so using actual body weight to set tidal volume leads to dangerous overinflation. The Devine formula estimates ideal body weight (IBW) from sex and height: 50 kg plus 2.3 kg for each inch above 60 inches in males, or 45.5 kg plus 2.3 kg per inch in females. The ARDSNet trial uses a nearly identical "predicted body weight" (PBW) formula with a metric base (0.91 kg per cm above 152.4 cm). Both give very similar values and are interchangeable in clinical practice. All tidal volume targets on this calculator are expressed in mL per kg of IBW.
The ARDSNet lung-protective ventilation protocol
The landmark ARDSNet ARMA trial (2000) demonstrated a 22% reduction in mortality in ARDS patients ventilated with 6 mL/kg PBW compared with the then-standard 12 mL/kg. The protocol targets 4-6 mL/kg PBW with plateau pressure kept below 30 cmH2O. When plateau pressure exceeds this limit, the volume is reduced in 1 mL/kg steps down to a minimum of 4 mL/kg. Permissive hypercapnia (accepting a higher arterial CO2 in exchange for lower volumes and pressures) is a core feature of the protocol. Outside of ARDS, the widely accepted safe initial setting for any mechanically ventilated patient is 6-8 mL/kg IBW, with 6 mL/kg increasingly preferred as a default to limit ventilator-induced lung injury (VILI) even in patients without formal ARDS criteria.
Minute ventilation and alveolar ventilation
Minute ventilation (MV) is tidal volume multiplied by respiratory rate. A patient set to 500 mL at 14 breaths per minute has a minute ventilation of 7 L/min, squarely within the normal adult range of 5-8 L/min. Alveolar ventilation excludes dead space: alveolar VE = RR x (TV - dead space), where dead space is roughly 150 mL in adults. CO2 clearance depends on alveolar ventilation, so a clinician adjusting for hypercapnia can increase either rate or volume, but increasing volume is more efficient because it reduces dead-space fraction. The minute ventilation figure in this calculator gives a quick sanity check that the chosen settings will deliver physiologically adequate ventilation at the selected respiratory rate.
Tidal volume targets by clinical context
| Clinical context | TV target (mL/kg IBW) | Rationale |
|---|---|---|
| ARDS (severe, P/F < 100) | 4-5 | Ultra-protective; allows permissive hypercapnia |
| ARDS (moderate/mild, P/F 100-299) | 4-6 | ARDSNet protocol; reduces VILI, improves survival |
| Acute lung injury at risk | 6 | Standard ARDSNet lung-protective goal |
| Post-operative / routine MV | 6-8 | Conventional initial setting; watch plateau pressure |
| Normal spontaneous breathing | 5-7 | Physiologic range at rest (~500 mL in healthy adult) |
| During exercise (spontaneous) | 2,000-3,000 | Can rise 4-6x resting value during heavy exertion |
Summary of recommended mL/kg IBW targets by clinical indication. Always confirm with current institutional protocols and arterial blood gas results.
Frequently asked questions
What is the normal tidal volume for an adult?
In a healthy adult breathing quietly at rest, tidal volume is approximately 500 mL, or 5-7 mL per kilogram of ideal body weight. Men average slightly higher than women because of their larger lung volumes. During exercise, tidal volume can rise to 2,000-3,000 mL as the accessory muscles of respiration are recruited.
Why does this calculator use IBW rather than the patient's actual weight?
Lung size is determined by the height and skeletal frame of the patient, not their total body mass. An obese patient's lungs are no larger than those of a lean person of the same height. Setting a ventilator using actual body weight in an obese patient would deliver far more volume than the lungs can safely accommodate, causing barotrauma and volutrauma. Using IBW (or the nearly equivalent ARDSNet PBW) scales the tidal volume to the actual lung capacity.
What does 6 mL/kg IBW mean?
6 mL/kg IBW means the ventilator delivers 6 millilitres of air for every kilogram of the patient's ideal body weight with each breath. For a patient with an IBW of 70 kg, this gives 420 mL per breath. The ARDSNet protocol showed that keeping tidal volume in the 4-6 mL/kg IBW range reduces mortality in ARDS, and this target is now widely used as a starting point for any patient on mechanical ventilation.
When should I use 4 mL/kg versus 6 mL/kg versus 8 mL/kg?
4-6 mL/kg IBW is the ARDSNet lung-protective target for ARDS and acute lung injury. 6 mL/kg is the most widely recommended default starting point for general mechanical ventilation. 6-8 mL/kg is acceptable for routine post-operative ventilation in patients with healthy lungs, provided plateau airway pressure stays below 30 cmH2O. Values above 8 mL/kg should be avoided unless specifically indicated, as overdistension injures alveoli even in normal lungs.
What is plateau pressure, and how does it relate to tidal volume?
Plateau pressure (Pplat) is the airway pressure measured at end-inspiration when airflow is zero - it reflects the elastic recoil of the lung and chest wall and is a proxy for alveolar distending pressure. The ARDSNet protocol targets Pplat below 30 cmH2O. If Pplat exceeds this threshold, tidal volume should be reduced by 1 mL/kg steps regardless of where you started, down to a minimum of 4 mL/kg. This calculator does not measure Pplat directly - a bedside respiratory therapist or ventilator display is needed.
Does this calculator account for endotracheal tube depth?
No. ETT depth is estimated separately with the Chula formula (ETT depth in cm = 0.1 x height in cm + 4, measured from the right upper canine). The MDCalc ETT Depth and Tidal Volume Calculator combines both calculations if you need tube depth alongside volume. This calculator focuses exclusively on tidal volume and minute ventilation from IBW.
How is tidal volume measured in spontaneously breathing patients?
In spontaneously breathing patients, tidal volume is measured during spirometry while the patient breathes quietly and normally. A flow sensor or pneumotachograph connected to a mouthpiece records airflow over time; the integrated signal gives volume per breath. In mechanically ventilated patients, the ventilator displays both set (inspiratory) and measured (expiratory) tidal volume continuously, and the difference between the two highlights any circuit leak.