Landscaping materials like soil are typically measured using the cubic foot (CF) as the standard unit for volume. Understanding how a cubic foot translates into physical weight and financial expense is necessary for planning any successful project. This article clarifies these measurements, providing the necessary context for purchasing soil.
Defining the Volume of a Cubic Foot
A cubic foot (CF) is a unit of volume defined as the space occupied by a cube measuring 12 inches long, 12 inches wide, and 12 inches high. This unit provides a consistent measure for materials like topsoil, compost, and mulch. For reference, a cubic foot is roughly the size of a standard kitchen microwave.
Factors That Determine Soil Weight
The weight of a single cubic foot of soil is highly variable, generally ranging between 70 and 100 pounds. This variation is due to the physical properties of the material itself. The primary factors influencing the final weight are the soil’s composition and its moisture content.
Soil composition directly affects density, with different soil types weighing substantially more than others. Clay-heavy soils and subsoil, which contain tightly packed fine particles, tend to be denser and fall toward the higher end of the weight range. Lighter materials, such as potting mixes or soils rich in organic matter and peat moss, have more air space and will weigh less per cubic foot.
The presence of water is the single greatest determinant of soil weight. Dry soil is significantly lighter than moist or wet soil because water molecules add substantial mass to the material. A cubic foot of completely saturated soil can reach 100 pounds or more, while the same volume of dry, loose topsoil might weigh closer to 75 pounds.
Estimating the Cost of Soil
The cost of a cubic foot of soil fluctuates based on three main commercial factors. These include the method of purchase, the quality of the material, and the inclusion of delivery fees. Understanding these variables helps consumers make cost-effective choices.
The purchasing method creates the largest price difference, as soil is sold either in small bags or in bulk by the cubic yard. Buying soil in bulk from a local landscape supplier is almost always cheaper per cubic foot than buying multiple small bags. One cubic yard contains 27 cubic feet.
Specialized soil quality or type also influences the price point dramatically. Standard fill dirt or basic screened topsoil is the least expensive option, but premium materials command a higher price. Products like sterilized potting mix, custom garden blends, or enriched compost mixes contain specific amendments and processing, which increases their overall cost per cubic foot.
The cost of transporting the material can drastically increase the final expense, especially for small orders. Bulk orders require a delivery truck, and the associated delivery fee is often a flat rate regardless of the volume ordered. This fee might be a significant portion of the total cost for just one cubic yard, but it becomes negligible when spread across larger volumes.
Calculating Project Coverage
The cubic foot measurement is the foundational unit used to calculate how much soil is required to cover a specific area at a desired depth. Project coverage is determined by multiplying the length and width of the area by the depth, with all measurements converted to feet. A simple rule of thumb for quick estimates is that one cubic yard covers 100 square feet at a depth of approximately three inches.
Calculating Volume
To determine the volume of soil needed, first calculate the square footage of the area to be covered. Next, convert the desired depth in inches to a fraction of a foot by dividing the depth by 12. For instance, a four-inch depth is equal to 4/12, or 0.33 feet. Multiplying the total square footage by the depth in feet yields the total cubic feet required for the project.
Example Calculation
For example, a garden bed measuring 10 feet by 10 feet needs 100 square feet of coverage. If the project requires four inches of soil, multiplying 100 square feet by 0.33 feet equals 33 cubic feet of soil required. Since bulk is generally sold by the cubic yard (27 cubic feet), this project would require slightly more than one cubic yard.