Most gravel suppliers sell gravel by the cubic yard, although some sell by weight. To calculate the cubic yards of gravel necessary for a driveway, first multiply the length of the driveway in feet by the width in feet. The result is the surface area of gravel needed for the driveway. Multiply this result by the desired depth of gravel also expressed in feet. For example, a depth of 3 inches would be 0.25 foot and 6 inches would be 0.5 foot.

Multiplying the length by the width by the depth gives the amount of gravel needed in cubic feet. To arrive at cubic yards, divide the amount by 27, the number of cubic feet in a cubic yard. As an example, the cubic yards of gravel needed for a driveway that is 48 feet long and 9 feet wide at a depth of 3 inches would be 48 x 9 x 0.25 = 108 cubic feet. Divide 108 by 27 to arrive at 4 cubic yards of gravel.

If the gravel dealer sells gravel by weight, find the weight per cubic yard of the type of gravel you plan to use, and multiply it by the number of cubic yards you calculated.