According to the University of New Hampshire, it takes 500 years to make an inch of topsoil. Water and poor gardening practices easily removes this precious layer of soil form the top of gardens and lawns. Adding topsoil to a garden or lawn can drastically approve the quality of the plants and landscape. Calculating how much top soil that is needed in an area requires a few measurements and some basic multiplication.
Measure the length and width of your lawn and multiply them together to get the area of your lawn. If the area is a circle, measure the diameter of the circle and divide the sum by 2. Square the sum of the circle and divide it by pi (3.14) to get the surface area.
Decide how deep you need the topsoil to be. Consider which plants you are growing.
Multiply the sum from the first calculation by how many yards deep you require the topsoil to be to get the cubic yards required for your lawn. If your lawn is 50 feet wide by 50 feet long, you would multiply 2,500 by, say, 0.02 yards deep, which would equal 50 cubic square feet of top soil.