How to Calculate Topsoil for Your Lawn or Garden
Calculating the amount of topsoil, compost, or mulch you need for a landscaping project requires finding the total cubic volume of the area. Bulk landscaping materials are universally sold by the cubic yard, while bagged topsoil is typically sold in cubic feet (usually 0.75 or 1 cubic foot per bag).
- L = Area Length (in feet)
- W = Area Width (in feet)
- D = Desired Depth (in inches)
Note: Dividing the depth in inches by 12 converts it to feet. Dividing the total cubic feet by 27 converts the final volume to cubic yards.
If you are trying to decide whether to buy bagged dirt or order bulk delivery, remember that 1 cubic yard equals 27 cubic feet. It takes exactly thirty-six 40-pound bags (0.75 cu ft each) to equal a single cubic yard of bulk topsoil.
| Soil Depth (Inches) | Coverage Area (Square Feet) | Common Application |
|---|---|---|
| 1 inch | 324 sq ft | Top-dressing established lawns. |
| 2 inches | 162 sq ft | Reseeding or patching sparse grass. |
| 3 inches | 108 sq ft | Mulching existing flower beds. |
| 4 inches | 81 sq ft | Establishing a new lawn or garden bed. |
| 6 inches | 54 sq ft | Deep raised garden planters and vegetable beds. |
Frequently Asked Questions
How deep should topsoil be for a new lawn?
For planting a healthy new lawn, a minimum depth of 4 to 6 inches of quality, uncompacted topsoil is recommended. Grass roots need this depth of loose, nutrient-rich soil to properly establish themselves and survive hot weather. If you are just overseeding an existing lawn, 1/4 to 1/2 inch of top-dressing is sufficient.
Should I order bulk topsoil or buy bags?
As a general rule, if your project requires more than 1 cubic yard of dirt, it is significantly cheaper to order bulk topsoil delivery. Because one yard equals roughly thirty-six 40-pound bags, buying bagged soil quickly becomes both expensive and physically exhausting due to the excess plastic waste and handling required.
Does topsoil compress after it is laid?
Yes. Loose, freshly delivered topsoil will naturally compress and settle by approximately 10% to 20% after it is spread, watered, and walked upon. If you are calculating soil for deep raised beds or a large grading project, it is wise to order an extra 10% to account for this natural settling factor.