how deep should the post go into the ground?
how much post should be above ground?
So in total, how long should the post be?
That one appears to be out around 4 ft so a 6 ft post would be great. For your main signs, I would think the 8 foot posts would work with 18-24" in the ground. If it looks too tall just cut it once it's fastened in the ground.
@Louvie, thanks Ken!
Great post & answer!