Final answer:
For correct gavage feeding tube placement in a newborn, measure from the nose to the earlobe and down to the xiphoid process to estimate the length needed to reach the stomach.
Step-by-step explanation:
To determine the correct length of a feeding tube needed for gavage feeding of a newborn, the nurse should measure from the tip of the newborn's nose to the earlobe, and then down to the xiphoid process, which is just below the rib cage. This measurement provides an estimate of the distance from the nose to the stomach, ensuring that the tube is long enough to reach the stomach without coiling in the esophagus, but not so long that it irritates or perforates the stomach lining.