Various types of rock are used as construction and landscaping materials. For example, crushed granite is a convenient and inexpensive material for paving driveways and garden paths. It is necessary on such projects to figure out the cubic yards of material needed, and rock is usually sold in cubic yards. A cubic yard is a measurement of volume, rather than area, and it tells you how much material is needed to fill a space, instead of just covering the surface.
Measure the length and width, in feet, of the area to be covered.
Multiply the length by the width to get the square footage. For example, 20 feet multiplied by 10 feet is 200 square feet.
Measure the depth you want, in inches--how high you want the layer of crushed granite or other rock. Multiply this number by the square footage. For example, 200 square feet multiplied by 2 inches is 400.
Divide this by 324, the number of inches in a cubic yard (a cubic yard is 27 cubic feet). For example, 400 divided by 324 is 1.2 cubic yards.