Size marked on bronchoscope (I.D in mm)

External diameter (in mm)

Age range

2.5

4

Premature/Neonate

3

5

4 weeks - 3 months

3.5

5.7

4 - 12 months

4

7

12 - 36 months

5

7.8

3 - 9 years

6

8.2

Over 9 years