How much fill dirt to fill a hole12"x12'x12" in the center and from center radiating out to 0 depth?

How much fill dirt to fill a hole12"x12'x12"

A hole that is 1 foot by 12 feet by 1 foot has a volume of 12 cubic feet.


in the center and from center radiating out to 0 depth? Sorry, but I don't understand what you mean. Please clarify.

Sorry my typing error.
The hole is 12'x12'x12" deep at the center, rediating out to 0 deepth

If the bottom goes from 12 inches deep at the center of the trench to 0 inches at the two ends (as in the attached picture), then the volume of material needed to fill the trench is one half of what it would be if it was 12 inches deep throughout its length. So the total volume is 6 cubic feet.