How Much Dirt Do I Need?
(or how many cubic yards of soil do I need?)

A ton of dirt? 1 cubic yard of dry sand roughly weighs 1 ton (2,000 lbs).
1 yard = 3 feet
1 cubic yard = 27 cubic feet (3 feet x 3 feet x 3 feet)
1 cubic foot = 12 inches x 12 inches x 12 inches (or 1 foot by 1 foot by 1 foot).
A cube is an object that has 3 dimensions: width, length, and depth. So, when something is said to be cubed it means that it is measured in the 3 dimensions of width x length x depth.
On the other hand, a square casually refers to an object of 2 dimensions: width and length. When something is said to be "squared" it means it is measured in the 2 dimensions of width x height.
Cubic measurements are used for measuring volumes. Think of an ice cube, for example, it has 3 dimensions.
Square measurements are used for measuring areas. A house lot, for instance, may be said to be so many square feet. This refers to the area of the land that the house sits on.
A square yard and a cubic yard, what's the difference? A square yard is when you square two sides that measure 3 feet each. That is, 3 feet in width times 3 feet in length equals 9 squared feet (3 x 3 = 9). A cubic yard, as described above, is when you cube 3 feet. That is, 3 feet times 3 feet times 3 feet equals 27 cubed feet (3 x 3 x 3 = 27).