Most of the pre-made coax cables with connectors are going to be 18ft. That was enough to go from my tire carrier up to the center console with several feet of slack left on both ends. Running along the sides and then over to the center under the passenger seat. But I have a 2 door, so it's a shorter distance and unlimited.
Going up and all the way over to the rear view mirror area is probably a longer distance. You might want to measure it with a piece of rope or string first. Run the rope the same way you plan to run the coax and see how much it takes. You'll want to have 1-2ft of slack on each end for flexibility, repairs, changes, etc.
Despite what you may read or hear, you do not need 18ft, or multiples of 18ft. The correct length is shortest length with 1-2ft slack on each end. Multiples of 18ft only matter when co-phasing multiple antennas like truckers do.