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Tidal Volume Calculator

Get 6–8 mL/kg tidal volume targets from height and sex.

How it is calculated

Height is entered in centimetres and sex is chosen as male or female. The tool first converts height to inches, in = cm ÷ 2.54, and estimates ideal body weight (IBW) with the Devine formula: IBW = 50 + 2.3 × (in − 60) kg for males and IBW = 45.5 + 2.3 × (in − 60) kg for females. Tidal volume targets are then 6 × IBW and 8 × IBW in mL, rounded to whole millilitres. The calculation uses height and sex only, not the patient's actual weight. For heights below about 97 cm for males or 102 cm for females the formula would give a negative weight, so the tool shows 0. It is a reference calculation for trained staff, not a ventilator setting.

Worked example

A male patient is 175 cm tall. Height in inches: 175 ÷ 2.54 = 68.90. Inches over 5 feet: 68.90 − 60 = 8.90. IBW = 50 + 2.3 × 8.90 = 70.46 kg. Lower target: 6 mL/kg × 70.46 = 423 mL. Upper target: 8 mL/kg × 70.46 = 564 mL. The range is therefore 423 to 564 mL, whatever the patient's actual weight is. A female patient of 165 cm would have an IBW of 56.91 kg and a 341 to 455 mL range.

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Common mistakes

  • Using the patient's actual weight instead of ideal body weight. Targets here follow height and sex, so entering weight (or expecting it to scale the result) defeats the purpose.
  • Entering height in inches or metres. The field is centimetres; 1.75 would be read as a height under 2 cm and give 0.
  • Choosing the wrong sex. The female baseline is 4.5 kg lower, so the volume range shifts by about 27 to 36 mL.
  • Reading the output as an order or a prescription. It gives a calculated 6 to 8 mL/kg range; the clinician decides the actual setting from the patient's condition.
  • Applying the male or female Devine formula to children. This formula is built on adult height in inches above 5 feet and does not suit paediatric patients.

Sources

About this calculator

Tidal volume is the amount of air moved in a single breath, and in mechanical ventilation, using too large a tidal volume can overstretch and injure the lungs — a problem especially critical in patients with acute respiratory distress syndrome (ARDS). Lung-protective ventilation protocols, most notably the ARDSnet strategy, target roughly 6 to 8 mL per kilogram of ideal body weight (IBW), not actual body weight, since lung size correlates with height and sex rather than with fat mass.

Ideal body weight is estimated from height and sex using formulas such as the Devine formula, and the tidal volume target is then derived from that IBW rather than the patient's measured weight — meaning an obese patient and a lean patient of the same height receive the same target tidal volume. From height and sex it estimates ideal body weight and turns it into the 6 to 8 mL/kg tidal volume range clinicians use for lung-protective ventilator settings.

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