Selection of an optimal endotracheal tube size is crucial in pediatric patients  and are mainly done with the age , height based formula routinely  which fails to yield an accurate size ETT resulting in increase in need of reattempts in intubation causing acute and chronic airway injury . Ultrasound being one of the advanced, reliable  and feasible modality which helps in measuring appropriate ETT size. The aim of the study is to determine the accuracy of ultrasound to estimated the real-time ETT size and to prevent the  need of reintubation as it is dangerous to pediatric airway. Objectives of this study is :  To identify the accuracy of ultrasound in assessing the correct endotracheal tube size and to assess the number of attempts required to change the ultrasound estimated estimated endotracheal tube size based on air leak test. This is a hospital base case series study. Thirty ASA I-III patients of age 2-6 years under going elective surgery requiring general anaesthesia are choosen. After obtaining institutional  ethical clearance, written informed consent will be taken from patient’ s parents and guardians. After induction with general anaesthesia a real-time USG guided subglottic diameter will be measured. Initial ETT will be choosen according to measurement made using USG guidance and leak test is performed to determine the best fit ETT size. The study parameter are the external diameter(OD) of ETT and the  internal diameter of subglottic area measured by USG guidance.