A cubic yard is the standard volume measurement used when purchasing bulk landscaping materials like mulch. This unit represents the amount of material that would fill a cube measuring three feet long, three feet wide, and three feet high. Accurately determining the volume of mulch needed prevents the expense of over-ordering or the delay of under-ordering. The calculation involves three steps: measuring the surface area, selecting the required depth, and converting those dimensions into total cubic yards.
Determining the Area of Coverage
The first step in calculating the total mulch required is to find the surface area of the planting beds in square feet. For simple rectangular or square shapes, find the square footage by multiplying the length by the width. Ensure all measurements are taken in feet, as this simplifies the final volume calculation.
Many landscape beds have curved or irregular edges, requiring a different approach for accurate measurement. One effective method is to visually divide the odd shape into smaller, manageable regular shapes, such as rectangles, triangles, and semicircles. Calculate the area of each smaller shape using its specific formula, then add the individual totals together to find the overall square footage.
For complex, highly curved areas, you can use an estimation method involving a central axis line across the longest part of the bed. Along this line, measure the width perpendicular to the line at several equally spaced intervals (e.g., every three feet). Add these perpendicular width measurements together and multiply that sum by the distance between the intervals to estimate the total square footage.
Selecting the Appropriate Mulch Depth
Choosing the correct depth directly impacts plant health and material effectiveness. For most general landscaping and flower beds, a depth between two and four inches is recommended. This layer is sufficient to suppress weed growth by blocking sunlight and helps regulate soil temperature and conserve moisture by reducing surface evaporation.
Applying mulch too thinly (less than two inches) fails to provide adequate weed control or moisture retention. Conversely, applying mulch too thickly (beyond four inches) can suffocate plant roots by restricting air and water movement. Excessively deep mulch can also create a damp environment favorable for pests or lead to “mulch volcanoes” piled against tree trunks, causing stem rot.
Calculating Total Cubic Yards
With the landscape area measured in square feet and the desired depth selected in inches, combine these numbers to determine the total volume in cubic yards. The first step involves converting the area and depth measurements into a volume expressed in cubic feet. This requires converting the depth from inches into feet by dividing the chosen depth by 12.
The formula for the total volume in cubic feet is the area in square feet multiplied by the depth in feet. For example, a bed measuring 100 square feet with a three-inch depth means the depth in feet is 3 divided by 12, or 0.25 feet. The volume is then 100 square feet multiplied by 0.25 feet, resulting in 25 cubic feet.
The final step is converting the volume from cubic feet to cubic yards, as bulk mulch is sold by the yard. A cubic yard contains exactly 27 cubic feet of material. Divide your total cubic feet by the conversion factor of 27; for example, 25 divided by 27 equals approximately 0.926 cubic yards.
Since most suppliers do not allow ordering a fraction of a cubic yard, always round the final number up to the next whole number. It is also wise to calculate an additional five to ten percent beyond the base calculation. This buffer accounts for settling, uneven application, or minor spillage, ensuring the project is completed without needing a second delivery.