Endotracheal Tube (ETT) Size Calculator

The Endotracheal Tube (ETT) Size Calculator estimates the appropriate internal diameter and insertion depth for pediatric patients based on age and tube type. This tool helps healthcare providers determine the initial equipment size for airway management. Whether you are preparing for emergency intubation or a scheduled procedure, this calculator provides quick estimates based on standard PALS guidelines.

Enter age in years (0 to 18). Decimals allowed for infants.
Select whether using a cuffed or uncuffed endotracheal tube.

How Endotracheal Tube Size Is Calculated

This calculator uses the standard Pediatric Advanced Life Support (PALS) formula to estimate the uncuffed tube size, with an adjustment for cuffed tubes. The calculation relies primarily on the patient's age, which serves as a proxy for airway diameter in children.

Uncuffed Tube Size = (Age / 4) + 4

Cuffed Tube Size = (Age / 4) + 3.5

Where:

  • Age: Patient's age in years (for neonates, weight is preferred)
  • Tube Size: Internal diameter in millimeters (mm)

The insertion depth is estimated by multiplying the calculated tube size (in mm) by 3. This provides a target length from the teeth or lips to the mid-trachea. Cuffed tubes use a slightly smaller diameter than uncuffed ones because the cuff requires space within the airway, reducing the need for a tight fit.

While this formula provides a useful starting point, airway anatomy can vary. Healthcare providers should always have a smaller and a larger tube available as backup options during the procedure.

What Your ETT Size Means

The calculated tube size represents the internal diameter (ID) required to allow adequate airflow and ventilation while minimizing trauma to the tracheal mucosa. Selecting the correct size is critical for preventing air leaks (too small) or ischemia and difficulty suctioning (too large).

For Routine Intubation:

If the calculated size fits within standard ranges (e.g., 3.0 mm to 7.0 mm for children), use the calculated cuffed tube. This allows for lower inflation pressures and better protection against aspiration compared to uncuffed tubes. Verify the fit by listening for an air leak at 20-25 cm H2O pressure.

For Neonates (Age < 1):

If the patient is a neonate, uncuffed tubes were traditionally standard, but micro-cuffed tubes are increasingly used. For newborns, use the calculated size but verify against weight-based charts (e.g., 3.0 mm for ~3kg). The depth formula remains a useful estimate, but auscultation of bilateral breath sounds is mandatory.

Pro Tip

Always confirm depth placement with a chest X-ray after securing the tube. The ideal position is the tip of the tube located between the clavicles and the carina (T2-T4 level).

Disclaimer: This tool is for educational purposes only and does not replace clinical judgment. Always verify tube selection with direct visualization and confirm placement with auscultation and capnography. Consult PALS guidelines for specific patient needs.

Calculation logic verified using publicly available standards.

View our Accuracy & Reliability Framework →