Topsoil is the uppermost layer of the earth, characterized by a high concentration of organic matter and microbial life, providing necessary nutrients for plants to thrive. Landscaping and gardening projects frequently require bulk quantities of this material, which is traditionally measured and sold in a standard unit called the cubic yard (CY). This unit represents a fixed volume, allowing for consistent calculation of how much area a delivery will cover. Understanding this volume is the first step in accurately planning any project that involves spreading new soil.
The Basic Formula: Calculating Coverage
A cubic yard is a volumetric measurement equivalent to a cube three feet long, wide, and high, totaling 27 cubic feet. To determine coverage, this fixed volume must be converted into a unit compatible with the relatively shallow depths common in gardening, which are measured in inches.
Since one foot contains 12 inches, one cubic foot contains 1,728 cubic inches (12 x 12 x 12). Multiplying the 27 cubic feet by 1,728 results in a total volume of 46,656 cubic inches per cubic yard. The formula for calculating coverage is straightforward: the total volume in cubic inches divided by the desired depth in inches yields the area’s square footage.
Standard Project Depths and Coverage Examples
Applying the formula to common project depths provides a clear expectation of a cubic yard’s coverage capacity. For a light application, such as top-dressing a lawn or overseeding, a depth of one inch is recommended. At this shallow depth, one cubic yard can theoretically cover 324 square feet. This application introduces new nutrients or organic matter rather than significantly altering the existing grade.
For establishing a new flower bed, vegetable patch, or filling a small raised garden box, a depth of three inches is common. Applying one cubic yard at this thickness will cover 108 square feet. Projects involving major grading or establishing a new lawn base may require a six-inch depth. In this case, the cubic yard will cover 54 square feet, demonstrating how quickly the coverage area shrinks as the depth increases. These figures serve as the maximum theoretical coverage, assuming a perfectly even spread and no settling.
Factors Influencing Final Coverage
The calculated coverage figures represent an ideal rarely achieved in real-world application due to several physical and environmental variables. Compaction is a significant factor, referring to the soil’s tendency to consolidate after delivery and spreading. The loose, aerated state of topsoil when first delivered, often called “fluff,” quickly settles, causing the final depth to be less than the initial application.
The moisture content also heavily influences the volume and density upon delivery. Saturated soil will be heavier and may have already undergone compaction, resulting in a volume that takes up less space than drier material. Furthermore, the specific composition of the topsoil, such as a light loam or a heavier clay-based mix, affects its settle rate and ultimate density. Accounting for material lost during spreading, uneven application, and spillover is necessary when planning the purchase.
Determining Total Yards Needed
When planning a project, the most practical approach is to reverse the coverage calculation to determine the necessary total volume. The process begins by measuring the length and width of the area to establish the total square footage. Next, the desired depth in inches must be converted into a fraction of a foot by dividing the inches by 12. For example, four inches is equivalent to 0.33 feet (4 inches divided by 12).
To find the total cubic feet required, the measured square footage is multiplied by the depth in feet. If a garden bed is 10 feet long and 20 feet wide, the area is 200 square feet. At a four-inch depth (0.33 feet), the total volume is 66 cubic feet (200 x 0.33). The final step is converting this cubic footage into cubic yards by dividing the total cubic feet by 27. The 66 cubic feet needed converts to approximately 2.44 cubic yards, suggesting an order of three yards to accommodate settling and ensure full coverage.