Endotracheal Tube Size Calculator

Why Endotracheal Tube Size Matters

Choosing the correct endotracheal tube (ETT) size helps secure the airway without causing vocal cord trauma or air leaks during ventilation. An oversized tube can injure the larynx, while an undersized tube may not seal properly and can slip out of position. This calculator estimates uncuffed and cuffed internal diameters plus tip-to-lip insertion depth from patient age, following the same approach used in emergency and anesthesia references. For related pulmonary tools, see the CURB-65 Calculator and Dead Space Calculator.

Cole's Formula for Pediatric Patients

For children ages 1 to 12 years, Cole's formula is the most common age-based estimate for internal diameter (mm ID):

$$\text{Uncuffed size (mm)} = \frac{\text{age in years}}{4} + 4$$

$$\text{Cuffed size (mm)} = \frac{\text{age in years}}{4} + 3$$

Cuffed tubes are typically 0.5 to 1 mm smaller in internal diameter because the inflated cuff adds outer bulk. Insertion depth from the distal tube tip to the front of the lip is estimated as:

$$\text{Insertion depth (cm)} = \frac{\text{age in years}}{2} + 12$$

Neonates, Infants, and Adults

Newborns and infants under one year use standard reference sizes rather than Cole's formula alone. Neonates commonly receive a 2.5 mm uncuffed tube (1.5 mm cuffed) with about 10 cm insertion depth. Adults typically use 7.5 mm uncuffed or 6.5 mm cuffed tubes, though height and weight often guide final selection in older patients.

Cuffed tubes are preferred for most ages except very small newborns under about 3 kg, where uncuffed tubes are standard. Always confirm tube placement with bilateral breath sounds, capnography, and imaging when needed.