As you plan a landscaping project, one of the most common things a gardener must figure is the quantity of topsoil needed to complete the project. This mathematical equation requires you measure the area you will apply the topsoil and then figure the volume of the area to calculate the amount of topsoil you need. For best results, figure in a little extra to ensure you have enough topsoil to finish your project.
Measure the area you will apply the topsoil. Measure the length of the area and the width of the area in feet. If you have more than one area you are filling with topsoil, measure the length and the width of all areas. Write down the measurements.
Multiply the length and width of the first area and write this answer down. Multiply the length and width of any other areas and write these answers down. Add the answers together to find the total area to which you will be adding topsoil.
Determine the depth of the top soil you wish to apply. Common topsoil depths are 2 inches, 3 inches or 4 inches. Take the depth you desire in inches and divide it by 12 to convert the inches to feet. For example, if you wish to apply 2 inches of top soil, divide 2 by 12 to reach .16. If you wish to apply 3 inches of top soil, divide 3 by 12 to reach .25. If you wish to apply 4 inches of top soil, divide 4 by 12 to reach .33.
Multiply the answer in Step 2 by the converted answer in Step 3 to find the cubic feet of topsoil you require.
Convert the cubic feet to yards because most companies sell topsoil by the yard. Take the answer you found in Step 4 and divide this by 27 to convert to cubic yards.
Add 2 or 3 cubic yards to the total measurement you found in Step 5 to give you a little extra topsoil to work with.