The ideal proper position of the ETT was indicated when the distance from the tip of ETT to the carina and the distance from the upper border of the cuff of ETT to the vocal cords were found to be at least 2 cm.
Objective: To assess whether Chula formula can predict the proper length of orotracheal intubation.
Material and Method: This was a prospective study of 100 patients (50 males and 50 females) who underwent general anesthesia with orotracheal intubation. The Chula formula was used to calculate the length of endotracheal tube (ETT) at the right upper canine = 4 + (body height/10) cm. After intubation, a fiberoptic bronchoscope was inserted into the ETT to measure the distance from the tip of ETT to the carina and the distance from the upper border of the cuff of ETT to the vocal cords.
Results: The mean length of oratracheal tube at the right upper canine calculated by Chula formula was 20.8 cm in males and 19.6 cm in females. The mean distance from the tip of ETT to the carina was 4.1 cm in males and 3.0 cm in females. The mean distance from the upper border of the cuff of ETT to the vocal cords was 4.5 cm in males and 4.6 cm in females. There were 99 of 100 patients who had the tip of ETT was placed at least 2 cm cephalad to the carina, in only one female patient that the distance from the tip of ETT to the carina was found to be 1.9 cm. In every patient, it was found that the upper border of the cuff of ETT was placed at least 2 cm below the vocal cords.
Conclusion: In the present study, the Chula formula could be used to predict the proper length of orotracheal intubation in 99 of 100 patients.

Keywords: Length, Orotracheal intubation, Chula formula