I'm trying to determine how much concrete I'll need to set fence posts for a 6ft tall privacy fence. From what I've read these are the parameters I'll be using for each post hole.
Post: 4in x 4in x 8ft
Hole Diameter: 12in
Hole depth: 30in (6in of gravel + 24in for post)
When I calculate the concrete needed, do I use the 30in depth or just the 24in for the part of the post in the ground? At the moment I plan on using 3-50lb bags of sakrete fast drying per hole. Is this too much, too little, or just enough?