What size conduit should I use for Coaxial and Ethernet?
After a quick google search, I've estimated the dimensions of the cables as follows:


RG6 - diameter = 0.33", area = 0.08552 sq.in.
CAT6 = diameter = 0.25", area = 0.0491 sq. in.


So to run just these two cables, you're going to need 3/4" conduit (based on NEC Chapter 9 Tables). If you run two of each cable (4 total cables), you'll need 1" conduit. Three of each (6 total cables), you'll need 1 1/4" conduit.