Topsoil is essential for vigorous plant growth in your garden and is the backbone to a healthy lawn. Topsoil varies from only a few inches deep in rocky areas to several feet deep in parts of the Midwest. Topsoil contains organic material which helps plants thrive. Figuring out how many cubic yards of topsoil you need can be a little tricky and involves some mathematical calculations.
Multiply the length of the yard by the width to find out the square footage of the area. For example, a yard that is 20 feet wide by 20 feet long, has an area of 400 square feet.
Divide by 12 the number of inches of topsoil that you desire to add, to find out the depth expressed in number of feet. For example, if you desire 2 inches of topsoil over the entire area, divide by 12 to get a depth of 0.167 foot.
Multiply the number of square feet of the area by the depth of the topsoil expressed in number of feet, to find out the number of cubic feet of soil needed. For example, 400 square feet multiplied by 0.167 foot equals 66.8 cubic feet of topsoil.
Divide the number obtained by 27, to convert it cu cubic yards. For example, 66.8 cubic feet divided by 27 equals 2.47 cubic yards.