Correct pH probe placement is vital for the precision of esophageal pH monitoring. This study aimed at finding the optimal formula for placement of pH probe in the locus proposed by the European Society for Pediatric Gastroenterology, Hepatology, and Nutrition European Pediatric Impedance Working Group, that is, 2 vertebrae above the diaphragm. An analysis of data regarding 353 children ages 0-18 years in whom the position of the pH sensor was determined radiographically revealed that a mathematical formula (3.2 + 0.2 × body length or height, centimeter) could guide the probe to within 1/12 of thoracic spine length of the desired location in 71.7% of all of the patients.