Setting the breath size
On a ventilator, tidal volume is one of the main settings. Too large a breath can stretch fragile lungs; too small can leave carbon dioxide in the blood.
Respiratory physiology
Tidal volume, one breath at a time
Tidal volume is a basic number in breathing science and intensive care. This page defines it, gives the normal range, shows how it is calculated from height and explains how it fits among the other lung volumes.
≈ 500 mLadult at rest
6–8 mL/kgtypical target by ideal weight
≈ 6 L/minresting minute ventilation
What tidal volume means
With every quiet breath your chest takes in some air and lets it go again, like a small tide. The amount moved in a single such cycle is the tidal volume, abbreviated VT or TV.
It is only a part of what the lungs can hold. After a normal breath you can still breathe in a lot more, or push out a lot more, which is why physiologists split lung capacity into several named volumes.
Tidal volume rises with exercise, falls with shallow breathing and is one of the first values set when a person needs a ventilator.
Tidal volume calculator
Enter height and sex. The tool estimates ideal body weight with the standard Devine-style equations, then multiplies it by the chosen mL/kg value.
Formula for ideal body weight: men 50 kg + 0.91 × (height in cm − 152.4), women 45.5 kg + 0.91 × (height in cm − 152.4).
Tidal volume among the lung volumes
Four basic volumes add up to the total amount the lungs can hold. The figures are textbook averages for a healthy adult man, so individual values vary.
| Volume | Meaning | Approx. value |
|---|---|---|
| Tidal volume | Air moved in one quiet breath | ≈ 500 mL |
| Inspiratory reserve | Extra air you can breathe in after a normal inhale | ≈ 3000 mL |
| Expiratory reserve | Extra air you can push out after a normal exhale | ≈ 1100 mL |
| Residual volume | Air left in the lungs after the hardest exhale | ≈ 1200 mL |
Adding tidal volume and both reserve volumes gives the vital capacity, and adding residual volume gives total lung capacity.
Why tidal volume matters in care
Lung-protective approach
For conditions such as acute respiratory distress syndrome, guidelines favour a lower tidal volume, often around 6 mL/kg of ideal body weight.
Trends over single numbers
Teams look at tidal volume together with respiratory rate, oxygen levels, pressures and blood gases, not on its own.
From one breath to ventilation
Multiply tidal volume by the number of breaths per minute and you get minute ventilation. At 500 mL and 12 breaths a minute, that is 6 litres of air moving each minute.
Not all of that reaches the places where gas exchange happens. About 150 mL of every breath fills the airways, the dead space, and goes straight back out. The rest, the alveolar ventilation, is (tidal volume − dead space) × rate.
That explains why quick shallow breathing is inefficient: with a small tidal volume, a larger share of each breath is lost to dead space.
Frequently asked questions
What is tidal volume?
Tidal volume is the amount of air that moves into or out of the lungs during one normal, relaxed breath. In a healthy adult at rest it is about 500 millilitres.
What is a normal tidal volume per kg?
Clinicians usually aim for about 6 to 8 mL per kilogram of ideal body weight for ventilated adults. Lung-protective strategies often start near 6 mL/kg.
Why is ideal body weight used instead of actual weight?
Lung size depends mainly on height and sex, not on body fat. Using actual weight in a taller or heavier person would overestimate the safe breath size and could over-stretch the lungs.
What is the difference between tidal volume and minute ventilation?
Tidal volume is one breath. Minute ventilation is the total volume breathed in one minute, calculated as tidal volume multiplied by respiratory rate.
Can this calculator be used for treatment decisions?
No. It is an educational tool. Real ventilator settings are decided by trained clinicians who look at the whole patient.
Numbers become clear with practice
Try different heights and targets in the calculator and watch how minute ventilation changes.
Back to the calculator Read about tidal waves