How do I calculate the amount of landscape product I will need?

Here is the formula that we use to estimate the approximate amount of rock/dirt/mulch you will need:

Length x Width x Depth
divide by 27 = total cubic yards.
2'' deep use .17
3'' deep use .25
4'' deep use .33

Example: For an area 22 feet long by 3 feet wide and 3 inches deep: 22 x 3 x .25 divided by 27 = .61 cubic yards
Example: For an area 52 feet long by 6 feet wide and 4 inches deep: 52 x 6 x .33 divided by 27 = 3.81 cubic yards

1 cubic yard at 3'' deep covers an area 10 x 10 (approx.)