Cubic yards can be calculated by multiplying the length by the width by the height of a given volume. For such a calculation, all three measurements must already be in yards. When necessary, convert from feet to yards by dividing the number of feet by three.
There are 3 feet in a yard, and 12 inches in a foot; 1 yard, then, is equal to 36 inches. Convert from inches to yards by dividing the number of inches by 36.
One application for cubic yards is in loose garden and construction materials such as concrete, topsoil or mulch. For example, laying down 4 inches of topsoil on a 20 foot long by 35 foot wide would require 8.7 cubic yards of topsoil; 4 inches divided by 36 equals 0.1 yards, 20 feet divided by 3 equals 6.7 yards and 35 divided by 3 equals 11.7 yards.