A wide expanse of lawn extends across your front yard. Your grass looks awful and you've made the decision to rip it all up to amend the topsoil before reseeding. You've made a good choice but the sheer volume of topsoil needed to rehabilitate your front yard or garden makes your head spin. Learning how to calculate yards of topsoil needed will allow you to purchase the correct amount of soil to suit your yard size. Adding topsoil will improve your soil conditions and allow your yard or garden to become well established and healthy with proper care.

Determine the length and width of the area requiring topsoil with the measuring tape and make a note of these measurements.

Multiply the length times width to find the number of square feet of your planting area.

Measure the length and width of any areas such as walkways, driveways, paths and gardens that don't require additional topsoil. Multiply each length times width to determine square footage and add these figures together. Keep this number handy since this figure will be subtracted from your total topsoil requirements.

Decide the number of cubic yards of topsoil needed by determining the depth needed for your circumstances. New lawns require about 9 inches of new topsoil to aid grass seed germination. Vegetable and flower gardens require as much as 12 inches for best results. Topsoil is sold by the cubic yard. A cubic yard covers 36 square feet to a 9-inch depth and 27 square feet to a 12-inch depth.

Take the value of your square planting area and subtract any square footage from areas not requiring the addition of topsoil using the calculator. This value is your final square footage and will be used to calculate the amount of topsoil needed.

Divide the square footage by 36 to determine the amount needed for a 9-inch-deep layer or divide the square footage by 27 to find the amount needed for a 12-inch layer.