Fill Dirt vs. Topsoil: Differences, Uses & When to Use Which
One of the most common mistakes homeowners and DIYers make is choosing the wrong type of soil for their yard projects. Buying premium topsoil to fill a deep hole is an expensive waste of money. Conversely, planting grass directly into fill dirt is a recipe for lawn failure.
To ensure your projects stand on solid ground, let's look at the differences between fill dirt and topsoil.
What is Topsoil?
Topsoil is the outermost layer of the earth's surface, typically the top 2 to 12 inches. It is highly organic, containing decomposed leaves, grass, roots, and organic matter. This makes it rich in nutrients and microorganisms necessary for plant growth.
Primary Uses: Lawns, flower beds, vegetable gardens, and top-dressing grass patches.
What is Fill Dirt?
Fill dirt is the soil found beneath the topsoil layer. It is excavated from deeper in the ground and contains little to no organic material. Instead, it consists of clay, sand, gravel, and rocks. Because it lacks organic matter, it does not decompose, settle, or shift over time.
Primary Uses: Filling deep holes, building up retaining walls, grading around house foundations, and establishing structural base layers.
Key Differences and Comparison
| Feature | Topsoil | Fill Dirt |
|---|---|---|
| Organic Content | High (microorganisms, organic nutrients) | Low to None (mostly sand/clay) |
| Average Cost | Higher ($30 - $60 per cubic yard) | Lower ($10 - $25 per cubic yard) |
The Grading Rule of Thumb
If you are leveling an area or fixing the slope around your home to prevent basement leaks, never use topsoil. Because topsoil is loose and decomposes, water will easily seep through it, causing it to collapse. Instead, pack fill dirt tightly against the foundation to deflect water, and cover the top 3-4 inches with premium topsoil to allow grass to grow.
Frequently Asked Questions About Topsoil Volume
How do I calculate how much topsoil I will need?
Measure the length and width of the area in feet and the desired soil depth in inches. Multiply length by width, multiply by depth (in inches), and divide the total by 12 to find cubic feet. Divide by 27 to convert to cubic yards.
How much does a 40 lb bag of topsoil cover?
A standard 40 lb bag of topsoil contains approximately 0.75 cubic feet of soil. Spread at a 2-inch depth, one 40 lb bag will cover about 4.5 square feet.
Run Your Own Calculations
Apply these metrics directly to your yard layout using our Topsoil Calculator.
