Tidal Volume Calculator (predicted body weight, 6 mL/kg ARDSNet reference)

Understanding the tidal volume calculator — concept and principle

This calculator gives lung-protective tidal volumes for mechanical ventilation, scaled to predicted body weight (PBW) from height and sex. It shows the volume at a chosen target and at 4, 6 and 8 mL/kg PBW as a quick reference for clinicians and students.

mL per kg of ideal weight: with the default inputs the result is 396 mL (range 264–528 mL).

How it is calculated

PBW men (kg) = 50 + 0.91 × (height cm − 152.4)

PBW women (kg) = 45.5 + 0.91 × (height cm − 152.4)

Tidal volume (mL) = target mL/kg × PBW

The usual starting target is 6 mL/kg PBW; protocols allow 4–8 mL/kg.

The principle

Lung size depends on height and sex, not on body weight; a person who gains weight does not grow larger lungs. Using actual weight in heavier patients would over-stretch the lungs. Scaling to PBW gives volumes proportional to real lung size. The ARDS Network trial (2000) found lower mortality with 6 mL/kg PBW than with 12 mL/kg in acute lung injury and ARDS, which made this approach standard.

Worked example

Default inputs: height 170 cm, male, target 6 mL/kg.

PBW = 50 + 0.91 × (170 − 152.4) = 50 + 16.0 = 66 kg.
At 6 mL/kg: 6 × 66.0 = 396 mL.
At 4 mL/kg: 264 mL; at 8 mL/kg: 528 mL.

How to read the result

These volumes are starting points. At the bedside the team adjusts the setting using plateau pressure (kept under 30 cmH₂O), driving pressure, blood gases and the patient's breathing effort. The same height gives the same PBW whatever the patient weighs.

Common mistakes

Using actual body weight in obese patients.
Measuring height inaccurately; estimate from ulna or knee height if the patient cannot stand.
Applying adult formulas to children.

Keep in mind: This is a reference table, not a ventilator setting tool. Settings are chosen by the treating team.

Frequently asked questions

Why 6 mL/kg?

It reduced mortality compared with 12 mL/kg in the ARDS Network trial.

Is lung-protective ventilation used without ARDS?

Many units use 6–8 mL/kg PBW for most ventilated patients.

How is height measured in bed?

With a tape from heel to head, or estimated from ulna length.

Sources: The Acute Respiratory Distress Syndrome Network, "Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome", N Engl J Med 2000;342(18):1301–1308

Checked 9 Nov 2026. ARDS Network, “Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome”, N Engl J Med 2000;342(18):1301–1308 — PBW formulas, 6 mL/kg target, 4–8 mL/kg range and plateau pressure under 30 cmH₂O, as summarised in LITFL “ARDSnet ventilation strategy” (female constant 45.5 kg as in the ARDSNet protocol; standard value).

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