The weight of a volume of “dirt,” more accurately called soil, is not a fixed number but a variable influenced by several physical properties. This variability explains why a bag of potting mix feels light while an equal volume of wet clay is surprisingly heavy. The material occupying the constant five-gallon volume changes its weight dramatically based on its composition, density, and, most importantly, its water content.
The Quick Answer and Average Estimate
For a practical estimate, a five-gallon volume of typical, moderately moist garden topsoil generally weighs between 40 and 55 pounds. This range accounts for the average density of topsoil you would purchase in a bag or receive from a local supplier. To place this volume into a standard measurement used in soil science and construction, five US liquid gallons is equivalent to approximately 0.668 cubic feet.
The standard unit for measuring soil density is pounds per cubic foot (lbs/ft³). Average dry, loose topsoil falls around 75 to 90 lbs/ft³. Using the mid-point of this range, a five-gallon quantity of dry topsoil would weigh around 50 pounds, supporting the general estimate.
How Soil Composition Affects Weight
The solid material within the soil, known as the soil texture, significantly impacts its bulk density. Soil is broadly categorized by the proportion of sand, silt, and clay particles it contains.
Sandy soil particles are relatively large and irregular, which means they do not pack tightly, leaving more air space and resulting in a lighter density, often around 80 to 100 lbs/ft³. In contrast, clay soil is composed of extremely small, flat, plate-like particles that can fit together very tightly when compacted. This close arrangement minimizes the air pockets within the soil structure, leading to a much higher density and weight, often reaching 100 to 120 lbs/ft³ even before saturation. Specialized products like potting mix are the lightest, however, because they contain low-density organic materials like peat moss, perlite, and vermiculite, resulting in a bulk density as low as 40 to 60 lbs/ft³.
The Significant Impact of Moisture Content
Water content is the most significant factor determining the final weight of any given volume of soil. For reference, one US gallon of water weighs about 8.34 pounds. Soil acts like a sponge, and a five-gallon volume can absorb a substantial amount of water, which is then added directly to the total mass.
The difference between dry soil and waterlogged soil can result in a weight increase of 50% or more. For example, the difference between dry topsoil at 75 lbs/ft³ and wet clay at 120 lbs/ft³ is over 45 lbs per cubic foot, which is a major weight change for a small volume. Saturated soil, where nearly all pore spaces are filled with water, creates the heaviest possible scenario for that specific soil type.
A five-gallon volume of soil that shifts from being completely dry to fully saturated can easily increase in weight by more than 25%. This dramatic difference highlights why the weight of the water alone must be considered, as it can quickly overload a vehicle or project structure during transport.
Converting Volume Measurements for Projects
When planning larger projects, soil is bought and sold by volume in cubic feet or cubic yards, making the conversion from a small five-gallon measure important. One cubic foot of average topsoil weighs between 75 and 90 pounds, depending on its moisture level. This means a cubic yard (27 cubic feet) will weigh around 2,000 to 2,400 pounds, or approximately one ton.
For those needing a precise weight, a simple method is to use a smaller, known volume, such as a one-gallon container. By filling the container with the soil and weighing it, then subtracting the empty container’s weight, you can find the soil’s specific weight per gallon. Multiplying this figure by five provides an accurate weight for a five-gallon quantity of that particular material, accounting for its unique composition and current moisture level.