For endotracheal tube diameter: 2.5 mm for infants < 1000 g or < 28 weeks gestation 3 mm for infants 1000 to 2000 g or 28 to 34 weeks gestation 3.5 mm for infants > 2000 g or > 34 weeks gestation For insertion depth, the marker at the lip should typically be at 5.5 to 6.5 cm for infants who weigh < 1 kg 7 cm for infants who weigh 1 kg 8 cm for infants who weigh 2 kg 9 cm for infants who weigh 3 kg Many endotracheal tubes have insertion markings to be positioned at the level of the vocal cords to guide the initial placement.