I have a yard to level but find it a little hard to determine how much fill dirt will be needed. I had a helper estimate that we would need 100 yds of dirt. However, after searching the internet it seems we need to multiply L x W x D. The yard has a huge slope. The deepest area is about 3 ft below the visible portion of the foundation. While other areas are within 16 inches. What's the best way to determine the amount of fill dirt needed? If I follow the formula above, I came to 2,500 ft. My measurements were 63'L x 21W' x 2' (average depth from three measuring points). Is that right? The idea is to level the yard with the visible portion of the foundation as much as possible.