Definition
Topsoil is the upper, outermost layer of soil, typically the top 2-8 inches, which has the highest concentration of organic matter and microorganisms. Topsoil is where most biological soil activity occurs and is essential for plant growth. In construction and landscaping, topsoil is often removed before excavation and stored for later replacement. Quality topsoil should be dark, crumbly, and free of debris, rocks, and contaminants.
Formula
For lawns, a minimum of 4-6 inches of quality topsoil is recommended. For gardens, 8-12 inches is preferred. A cubic yard of topsoil covers approximately 324 square feet at 1 inch deep, 162 square feet at 2 inches deep, or 108 square feet at 3 inches deep. Topsoil compacts approximately 10-15%, so account for this when ordering.
Example
Topsoil Calculation Example
For a new lawn measuring 50x80 feet with 6 inches of topsoil: Area = 4,000 sq ft. Volume = 4,000 x 0.5 = 2,000 cubic feet. Converting to cubic yards: 2,000 / 27 = 74 cubic yards. For leveling existing lawns, 1-2 inches of topsoil is usually sufficient. For new construction, strip existing topsoil before building and replace it at final grade.