Topsoil, the uppermost layer of earth rich in organic matter and nutrients, is essential for preparing new lawns, filling garden beds, or amending existing soil conditions. Since topsoil is sold in bulk, its coverage is measured by volume, not weight, which can fluctuate significantly based on moisture content. The actual square footage a single unit of topsoil covers depends entirely on the required depth of the application.
What is a Cubic Yard of Topsoil?
Topsoil is typically sold by the cubic yard, a fixed unit of volume. A cubic yard is defined as a volume measuring three feet by three feet by three feet, which equates to exactly 27 cubic feet. This volume is constant regardless of the soil type, ensuring a standardized measure for bulk purchases. Unlike weight, which can vary by as much as 1,000 pounds per yard depending on how wet the soil is, the cubic yard remains a reliable unit for ordering.
Different landscaping applications require specific depths to be successful, dictating how far the material will spread. For example, a shallow application of half an inch is sufficient for light lawn topdressing. Conversely, a new raised vegetable bed may require a depth of 12 to 18 inches.
Calculating Coverage Area
Determining the exact amount of topsoil needed requires a straightforward calculation that converts the desired area and depth into cubic yards. Begin by measuring the length and width of the area to find the total square footage. This measurement is then combined with the intended depth of the topsoil layer, which should be determined based on the project’s goal, such as 4 inches for a new lawn or 6 inches for a garden.
The mathematical formula used to calculate the necessary cubic yards is: (Area in Square Feet \(\times\) Depth in Inches) \(\div\) 324. The constant 324 is the conversion factor that accounts for the 27 cubic feet in one yard multiplied by the 12 inches in one foot. For instance, if you have a 400 square foot area (20 feet by 20 feet) requiring a 3-inch depth, the calculation results in an order requirement of approximately 3.7 cubic yards of topsoil.
Coverage Estimates for Common Depths
For quick reference, one cubic yard of topsoil covers a specific square footage depending on the depth of the application.
At a shallow depth of one inch, one cubic yard covers approximately 324 square feet. Doubling the depth to two inches halves the coverage area, covering about 162 square feet. This inverse relationship continues as the thickness increases, providing smaller coverage for deeper applications.
For establishing a new lawn, which requires a depth of 3 to 4 inches, one cubic yard covers 108 square feet or 81 square feet, respectively. For deeper spaces, such as a low-profile raised bed requiring 6 inches of topsoil, a single cubic yard covers about 54 square feet.
It is recommended to order an additional 5 to 10 percent more material than the calculation suggests. This buffer accounts for factors like uneven subgrades, settling, and compaction after spreading.