Calc Function

    • Calcs that help predict probability of a diseaseDiagnosis
    • Subcategory of 'Diagnosis' designed to be very sensitiveRule Out
    • Disease is diagnosed: prognosticate to guide treatmentPrognosis
    • Numerical inputs and outputsFormula
    • Med treatment and moreTreatment
    • Suggested protocolsAlgorithm





    Chief Complaint


    Organ System


    Patent Pending

    Endotracheal Tube (ETT) Depth and Tidal Volume Calculator

    Estimates depth of optimal ETT placement and target tidal volume by height.


    Use in patients over 20 years old.

    When to Use
    Why Use

    Adult patients requiring orotracheal intubation.

    • ETT depth is measured based on the patient’s front teeth (not the molars).
    • Larger tidal volumes may be temporarily required for patients with severe metabolic acidosis.
    • Placing the ETT too deeply may cause right mainstem intubation, hypoxemia, and pneumothorax. However, placing the ETT too shallowly may risk injury to the vocal cords and accidental extubation. Standard approaches to verify ETT depth (e.g. bilateral auscultation) are insensitive.
    • Use of lower tidal volumes appears to prevent the development of acute respiratory distress syndrome, even in patients who do not have lung injury.


    Please fill out required fields.

    Next Steps
    Creator Insights


    • ETT position should still be verified with a chest radiograph among patients who will remain intubated for an extended period of time.
    • Tidal volume: 6-8 mL/kg ideal body weight (IBW) is generally a safe initial setting, but further ventilator adjustment may be required depending on the adequacy of ventilation and airway pressures.


    Endotracheal intubation and mechanical ventilation.

    Critical Actions

    Chest radiograph and measurement of CO2 level (e.g. end-tidal CO2 or blood gas analysis) to confirm ETT position and adequacy of ventilation.


    Chula formula: ETT depth = 0.1 * [height (cm)] + 4

    Additional formulas:

    • Ideal body weight (IBW), men = 50 kg + 2.3 * [height (in) – 60]
    • IBW, women = 45.5 kg + 2.3 * [height (in) – 60]
    • Usual tidal volume target = 6-8 mL/kg IBW

    Evidence Appraisal

    The Chula formula was developed and validated by Techanivate and colleagues at King Chulalongkorn Memorial Hospital in Thailand.

    These authors prospectively validated the use of this formula among 100 patients in Thailand. Patients were intubated and the ETT placed according to the formula. Subsequently, a bronchoscope was used to determine the relationship among the ETT, carina, and vocal cords:

    • The distance between the ETT and carina ranged between 1.9-7.5 cm. No patient was at immediate risk of endobronchial intubation.
    • The upper border of the ETT cuff was always >1.9 cm below the vocal cords, avoiding risk of laryngeal trauma or inadvertent extubation.

    Pak et al in 2010 and Hunyady et al in 2008 developed similar assessments of optimal ETT placement. The average of the three scores (Pak, Hunyady, and Chula) is nearly identical to the Chula formula.


    Dr. Anchalee Techanivate

    About the Creator

    Anchalee Techanivate, MD, is an associate professor in the Department of Anesthesiology at King Chulalongkorn Memorial Hospital of Chulalongkorn University in Bangkok, Thailand.

    To view Dr. Anchalee Techanivate's publications, visit PubMed

    Content Contributors
    • Joshua Farkas, MD
    About the Creator
    Dr. Anchalee Techanivate
    Partner Content
    Content Contributors
    • Joshua Farkas, MD