The weight of a cubic foot of “dirt,” scientifically known as soil, is highly variable. Soil is a complex mixture of minerals, water, air, and organic matter, all contributing to its mass. The weight depends entirely on its composition and current condition. This article establishes the general weight range for common soil and explains the primary factors causing fluctuation.
The Standard Weight Range for Dry Soil
A baseline weight can be established using common, loose, and dry soil, such as garden topsoil. A cubic foot of this material typically weighs between 70 and 100 pounds. This range represents the mass of the solid mineral and organic components before water is introduced into the pore spaces.
A cubic meter of this dry soil weighs approximately 1,120 to 1,600 kilograms (1.1 to 1.6 metric tons). This measurement is useful for initial calculations in construction or landscaping projects when the soil is relatively dry. This dry weight provides a starting point before accounting for the most significant variable: moisture.
The Impact of Moisture Content
Water is the single most influential factor on soil weight, as it fills the porous spaces between particles. One cubic foot of pure water weighs approximately 62.4 pounds, illustrating the substantial mass it adds. When soil absorbs water, it incorporates this weight without changing its overall volume.
The difference between dry and fully saturated soil can be dramatic, with wet soil potentially weighing 25% to 50% more. For example, an 80-pound cubic foot of dry soil could easily weigh 120 pounds or more when saturated. This increase explains why soil moved after heavy rain is substantially heavier and more difficult to handle.
Calculating Weight Based on Soil Type and Compaction
The inherent structure of the soil, determined by particle size, dictates its dry weight and capacity to hold water. Soil is primarily composed of sand, silt, and clay, and the proportion of these components affects density.
Soil Type
Sandy soil, having larger, denser particles and less pore space, is generally heavier when dry, often weighing around 95 pounds per cubic foot. Clay soil is typically lighter when dry but has a higher capacity for water absorption due to its microscopic particle size. Loam, a balanced mix of all three components, represents a common middle-ground density.
Compaction
The degree of compaction significantly increases the mass of soil within a fixed volume. Tightly packed soil, such as excavated fill, eliminates air pockets and can weigh more than loose topsoil, sometimes reaching 110 to 140 pounds per cubic foot.
Practical Estimation for Large Projects
For large-scale projects, soil is typically measured and sold in cubic yards (27 cubic feet). A cubic yard of common, loose, dry topsoil generally weighs between 2,000 and 2,100 pounds. This means a cubic foot of dry material averages about 74 to 78 pounds.
A quick estimation method uses a range of 1 to 1.5 tons per cubic yard. This broader range accounts for variability in soil type and moisture content, with the higher end representing saturated material. Understanding these weights is important for safety, as a full cubic yard of wet soil can weigh up to 3,000 pounds when loading hauling equipment.