Accurately calculating the amount of soil or dirt needed for a gardening or landscaping project is a practical necessity. Ordering the correct quantity prevents unnecessary expense from over-ordering and avoids project delays caused by under-ordering. This guide provides the practical steps necessary to translate your physical project dimensions into the precise volume required for your materials supplier.
Understanding the Unit of Measurement
Dirt, soil, and other landscaping aggregates are typically sold by volume. This standardized approach accounts for the natural variations in material density and moisture content that would make weight an unreliable measure. The standard unit of measure used by material suppliers for bulk orders is the cubic yard.
A single cubic yard represents a volume equivalent to a cube measuring three feet long, three feet wide, and three feet high. This means one cubic yard contains exactly 27 cubic feet of material. To calculate the volume of material needed for any space, you must determine its length, width, and the required depth.
Using consistent units is important before beginning any calculation. All three measurements—length, width, and depth—must be converted into feet to ensure the final result accurately reflects the volume in cubic feet, which can then be converted into cubic yards.
Calculating Volume for Standard Shapes
The simplest scenario involves areas that are rectangular or square. Begin by measuring the length of the area using a standard tape measure, recording the result in feet. Then, measure the width of the area, also ensuring this measurement is recorded in feet.
The third measurement required is the depth, which is the height of the material you plan to add. If you intend to fill a six-inch-deep raised bed, for example, that six-inch measurement must be converted into feet before calculation. The fundamental calculation for volume is simply multiplying the length by the width by the depth.
Once you have the length, width, and depth all expressed in feet, multiply them together to find the total volume in cubic feet. To convert this cubic feet measurement into the cubic yard, you divide the total cubic feet by 27. The resulting number is the exact number of cubic yards of material required for your project.
For example, a garden area measuring 10 feet long by 5 feet wide that needs 0.5 feet (six inches) of soil would require 50 cubic feet of material. Dividing 50 cubic feet by 27 results in a requirement of approximately 1.85 cubic yards. This simple formula provides a direct and accurate order quantity for standard-shaped projects.
Measuring Irregular Spaces and Final Adjustments
Landscaping projects often involve spaces that are not perfectly square or rectangular, such as curving borders or oddly shaped planting beds. To accurately measure these irregular areas, the best approach is to segment the space into a series of smaller, more manageable geometric shapes. You can divide the area into separate rectangles, squares, or even triangles.
Calculate the volume for each of these smaller, standardized sections individually using the length times width times depth formula. Once all sections have been calculated, simply add the volumes of the individual segments together to find the total volume for the entire irregular space.
A common measurement issue is that the required depth is usually taken in inches, which must be converted to decimal feet for use in the volume formula. To convert inches to a decimal foot measurement, divide the number of inches by 12. For instance, a four-inch depth is equal to 4 divided by 12, or approximately 0.33 feet.
After you have calculated the final volume for your project, it is advisable to add a small contingency factor to the order. Soil and dirt naturally settle and compact after they are delivered and laid down, and minor miscalculations are common in real-world measurements. Adding an extra 5 to 10 percent to the final cubic yard total helps account for this compaction and ensures you do not run short before the project is complete.