The study assessed the accuracy of the APLS and NRP formulas for predicting oral endotracheal tube (ETT) depth in Chinese infants aged 1–12 months undergoing elective surgery and developed a new formula validated with a flexible intubation video endoscope (FIVE) where the tip of the tube was positioned 1 cm above the carina. In neonates, FIVE-depth was correlated with height (r=0.670, P<0.001), weight (r=0.488, P<0.001) and body surface area (BSA). In infants 1–12 months, correlations were stronger with height (r=0.952, P<0.001), weight (r=0.895, P<0.001), BSA (r=0.926, P<0.001) and age (r=0.871, P<0.001). APLS and NRP formulas predicted a deeper depth than FIVE in 12.5% of neonates and 30.1% of older infants. The new formula for infants 1–12 months is: depth (cm) = 4.5 + 0.1 × height (cm). The weight-based APLS formula is less applicable to Chinese infants, while the height-based formula better corresponds to FIVE-depth. The model requires independent external validation before clinical use.