I have a 35 foot aluminum light pole that has 4 bolts holes in the base of the pole. I need to know how deep and wide should I pour the concrete into the ground. I'm not going to use the light pole for a light, I'm recycling it to make a flag pole. The base bolts holes are 8 inches apart in a square. The base bolts measure 11.5 inches diagonally. I want to be able to fly two flags from the pole and I want to make sure that I have enough concrete in the ground to support the pole, two flags, high winds, ect. I live in western Kentucky.
There are lots of variables that really need to be evaluated by a Registered Engineer but you can use this site for a quick evaluation:
Of course you'll need some details to figure the lateral force at the top of the pole, this comes from the size of the flag and the expected windspeed it will encounter. You'll also need a figure for the soil characteristics.
Again I encourage you to consult an engineer since the last thing you want is for this thing to come crashing down and injure or kill someone.