The amount of fill dirt needed when attempting to backfill an area depends on the shape of the area to be filled and can be calculated with only a calculator and tape measure. If filling a rectangular area, the length, width and depth of the area should be measured. If filling a circular area, only the diameter and depth of the area need to be measured.

According to SFGate, all measurements should be done in inches because fill dirt is sold by the cubic yard, which inches easily convert into. The amount of fill dirt needed for a rectangular area can be found by multiplying the length, width and depth of the area in inches. To find the number of cubic yards needed, the total should be divided by 46,656.

Similarly, the amount of fill dirt needed to fill a circular area can be found by first multiplying the square of the radius by the depth, and then multiplying that total by pi. Next, convert the total to cubic yards by dividing the result by 46,656. If the measurements are in feet, the number of cubic yards of fill dirt can be found by dividing the cubic feet by 27.