Size of DLT determined by width of trachea 

(bronchus is 2/3 trachea)

>18mm        41Fr

16-18           39

15-16           37

14-15           35                           

12.5-14        32

Depth of DLT determined by height:

5’9” is 29 cm deep.  

Add or subtract 1 cm depth for each increase/decrease of 4” in height