Objective: To investigate the relationship between age, sex, height, weight and body mass index (BMI) by measuring the subglottic diameter of the trachea (SDT) and its distance to the skin by ultrasonography (US) in children. Methods: This prospective study included a total of 234 children, 104 girls and 134 boys, with ages ranging from 3 to 17 years. Demographic data including sex, age, height, weight and BMI were recorded. The SDT and its distance to the skin was measured with a 14L5 high-frequency surface transducer. The correlation of SDT and its distance to the skin with basic descriptive data was investigated. Statistical analyses used were Mann–Whitney U, Kruskal–Wallis and Spearman correlation tests. Results: No significant difference was found among the median SDT and distance of the trachea from the skin values for boys (10.85 mm) and girls (11.15 mm) (p = 0.58). The distance of the trachea from the skin was greater in girls (5.5 mm) than in boys (4.75 mm) (p = 0.009). Median SDT values were 9.4 mm, 11.2 mm, and 13.35 mm in age groups 1, 2, and 3, respectively. There were highly significant strong positive correlations between SDT with age (p = 0.001, r = 0.78), height (p = 0.001, r = 0.76), and weight (p = 0.001, r = 0.70), and a highly significant moderate positive correlation between SDT with BMI (p = 0.001, r = 0.43). Median distance values of the trachea from the skin were 4.6 mm, 5.2 mm, and 6.2 mm in age groups 1, 2, and 3, respectively. There were moderate positive correlations between distance of the trachea from the skin with age (p = 0.001, r = 0.41), height (p = 0.001, r = 0.42), weight (p = 0.001, r = 0.53), and BMI (p = 0.001, r = 0.54). Conclusion: US is an accurate, safe, inexpensive, non-invasive and accessible method for objective evaluation of SDT and its distance to the skin. There is a positive correlation between age, height, weight, and BMI with SDT and its distance to the skin in healthy children.