I 'm a Newbie,,, I need to fill in where an above ground swimming pool once was and then seed. I am pretty sure a dirt hauling place could calculate this for me , however I would like to learn for myself. The old swimming pool hole is 21' diameter and 8'' deep. Can someone give me the formula on how much dirt i will need. If possible show me how it's calculated so i can use the formula for future references???? Thanks in advance.