Pediatric ETT Size Calculator

Choosing the right endotracheal tube (ETT) for a child matters: too small a tube leaks and raises airway resistance, while too large a tube can injure the subglottis, the narrowest part of the young airway. Age-based formulas give a quick starting estimate. This calculator applies the Cole formula for uncuffed tubes (age ÷ 4 + 4) and the widely used cuffed-tube formula (age ÷ 4 + 3.5), rounds down to the nearest available half-size, and lists the sizes to have ready either side.

It also estimates oral insertion depth at the lips in two ways: three times the tube’s internal diameter, and age ÷ 2 + 12 cm. Both are approximations; tube position must always be confirmed clinically and with capnography and, where appropriate, a chest radiograph.

The formulas are intended for children from 1 to about 10 years old. Infants and neonates are usually sized by weight and gestational age, and many children — including those with syndromes such as trisomy 21, airway disease or unusual size for age — need a different tube. Length-based resuscitation tapes are a common alternative. This tool is a reference for trained clinicians only.

Cole’s formula (age in years ÷ 4 + 4) is the long-standing rule for uncuffed tubes. Cuffed tubes have a thicker wall, so a half-size smaller tube is used: age ÷ 4 + 3.5 (the Motoyama/Duracher formula used in paediatric life-support teaching). Khine’s more conservative cuffed formula, age ÷ 4 + 3, is shown for comparison. Because tubes come in 0.5 mm steps, the result is rounded down to the nearest half-size.

Oral insertion depth at the lips is estimated as three times the internal diameter or as age ÷ 2 + 12 cm. These estimates assume a child of average size for age; final depth is set clinically.