Approximately 1 million enteral tubes are placed through the nose or mouth in adults and children in the United States annually. Previous studies found gastric tube placement errors to be common. A primary issue in ensuring safe and effective gastric feeding by tube is achieving optimal tube position on insertion. The purpose of this study is to use 24 variables to develop a clinical prediction rule for gastric tube insertion distance in adults, using the internal-nares-to-distal-lower esophageal-sphincter distance. A three-variable model using gender, weight, and nose-umbilicus-flat was selected. This new model, validated using nonparametric bootstrap cross-validation, correctly predicted gastric tube insertion distance 85.3% of the time. This new model is compared to two other methods, one evidence based and one commonly used in practice, and was found to be superior. Two nomograms, one for each gender, are drawn to make this new model easier to use.