Background: Proper sizing of endotracheal and tracheostomy tubes is essential for safe airway management. Ultrasonography offers a non-invasive method to assess airway anatomy, particularly the subglottic region. This study aimed to evaluate subglottic tracheal diameter and trachea-to-skin distance in healthy adults using ultrasound and to investigate their relationships with anthropometric variables. Methods: A prospective study was conducted on 178 healthy adults (92 males, 86 females) aged 18 to 65 years, grouped by age (18–35, 36–50, 51–65 years). Subglottic tracheal diameter and trachea-to-skin distance were measured using a Canon Aplio™ 300 ultrasound system with participants in a supine position. Height, weight, and body mass index were recorded. Statistical analysis included Mann–Whitney U test, ANOVA, and Pearson or Spearman correlation as appropriate. A p-value < 0.05 was considered statistically significant. Results: Males had significantly larger subglottic tracheal diameters than females (20.05 ± 3.01 mm vs. 16.93 ± 1.72 mm, p < 0.001). Trachea-to-skin distance showed no sex difference (p = 0.133) but increased significantly with age (p < 0.001), particularly between the youngest (8.12 ± 2.13 mm) and oldest (9.9 ± 2.5 mm) age groups. In younger adults, tracheal diameter correlated strongly with height (r = 0.65, p < 0.001), while trachea-to-skin distance correlated with both weight (r = 0.52–0.56) and body mass index (r = 0.50–0.64) across all age groups. Conclusions: Ultrasound provides a reliable and individualized assessment of airway anatomy. Subglottic tracheal diameter and trachea-to-skin distance vary with sex, age, and body composition, which may guide personalized airway management and tube size selection. Further clinical validation is warranted.