Age-based, weight-based and height-based categories with the corresponding optimal ETT tip-to-carina distance
| Category | Age (years) | Weight (kg) | Height (cm) | Average tracheal length (cm) | Optimal ETT tip-to-carina distance (cm) |
| 1 | 0–0.25 | >3–6 | >48–60 | 4.2 | 1.4 |
| 2 | >0.25–2.0 | >6–12 | >60–88 | 5.1 | 1.7 |
| 3 | >2–4 | >12–16 | >88–105 | 6.4 | 2.1 |
| 4 | >4–10 | >16–35 | >105–140 | 8.0 | 2.7 |
| 5 | >10–14 | >35–50 | >140–165 | 10.0 | 3.3 |
| 6 | >14–18 | >50 | >165 | 12.0 | 4.0 |
The optimal ETT tip-to-carina distance is defined based on the average tracheal lengths determined by Griscom and Wohl and Luscan et al; Conrardy et al recommend a target ETT tip position between the middle third and distal third of the trachea.14–16