Most lawn topsoil projects fall into one of two situations: you are fixing thin or bare spots on an existing lawn, or you are building a new lawn from scratch on bare ground. The depth you need is completely different in each case, and getting it wrong is expensive. Topsoil is heavy, delivery minimums are real, and returning a load you over-ordered is not an option.
Here is how to figure out exactly what you need before you call the supplier.
The formula
Topsoil is sold by the cubic yard. To find how many cubic yards you need:
Cubic yards = (length ft x width ft x depth in) / 324
The 324 comes from converting depth from inches to feet (divide by 12), then converting cubic feet to cubic yards (divide by 27). Since 12 x 27 = 324, you can skip two steps and divide by 324 directly.
How deep you actually need to go
This is where most people get the math wrong, and it changes the order size dramatically.
Topdressing an existing lawn: 1/4 to 1/2 inch. You spread a thin layer over existing grass to fill low spots, improve drainage, or prepare for overseeding. Thin enough that the grass can grow through it within two weeks.
Patching bare spots: 1 to 2 inches. Gives seeds a good rooting bed without burying the grass around the edges of the patch.
New lawn from seed: 4 to 6 inches. Grass roots grow deep and need soil depth to handle dry periods. Less than 4 inches and the lawn will look stressed every summer until the roots hit clay or rock and stop.
Raised areas or heavily amended beds: 8 to 12 inches if you want excellent drainage and deep rooting for a premium lawn.
A worked example
You have a 50 by 30 foot backyard that needs 4 inches of new topsoil before seeding.
- Cubic yards = (50 x 30 x 4) / 324
- = 6,000 / 324
- = 18.5 cubic yards
Add 15 percent for settling and low spots in the subgrade: 18.5 x 1.15 = 21.3 cubic yards. Round up to 22 yards.
For a topdressing project on the same lawn at half an inch deep:
- Cubic yards = (50 x 30 x 0.5) / 324
- = 750 / 324
- = 2.3 cubic yards
That is a completely different order size, which is why depth is the number that matters most.
Coverage reference by depth
| Depth | 1 cubic yard covers |
|---|---|
| 1/4 inch | 1,296 sq ft |
| 1/2 inch | 648 sq ft |
| 1 inch | 324 sq ft |
| 2 inches | 162 sq ft |
| 4 inches | 81 sq ft |
| 6 inches | 54 sq ft |
Bags vs bulk delivery
For small patches under about 3 cubic yards, bagged topsoil from the hardware store is convenient. A 40 lb bag holds roughly 0.75 cubic feet, so 36 bags equal one cubic yard. At $5 to $7 per bag, that works out to $180 to $250 per cubic yard when you buy in bags.
For anything larger, bulk delivery is far cheaper. Most suppliers sell topsoil at $25 to $55 per cubic yard depending on quality and your region, with delivery fees of $50 to $100. At 5 or more cubic yards, you recover the delivery fee quickly compared to buying bags.
Screened vs unscreened
Always order screened topsoil for lawn work. Screened topsoil has been sifted to remove rocks, clumps, and debris, and it spreads and rakes evenly. Unscreened topsoil is cheaper but you will spend an hour picking rocks out of it.
Some suppliers sell a “lawn mix” or “garden blend” that combines topsoil with compost. For seeding, this mix improves germination and the extra cost per yard is usually worth it on areas under 500 square feet. On larger areas, order straight topsoil and broadcast a thin layer of compost separately.
One tip before you order
Ask the supplier for a basic soil test on their topsoil, or test your existing soil first. If the pH of the new topsoil is significantly different from your existing soil, the new areas will look different from the old ones for several seasons. Matching pH, or amending at the time of install, prevents that problem.
Frequently Asked Questions
How deep should topsoil be for new grass?
A minimum of 4 inches of topsoil supports healthy grass roots. Six inches is better, especially in areas where the subsoil is clay-heavy or compacted. New construction sites are often stripped down to subsoil, and builders sometimes put only an inch or two back. If you can dig a fork into the ground easily to 4 inches, the depth is adequate. If you hit resistance at 2 inches, grass roots will too.
Can I just add topsoil on top of existing dead grass?
No, not without killing or removing the dead grass first. A thin layer of topsoil over dead turf creates a sterile mat that smothers new seed and prevents it from making root contact with the soil beneath. Kill the existing vegetation with herbicide or smother it with a thick layer of cardboard, wait for full decomposition, or rent a sod cutter to remove it before spreading topsoil.
What is the difference between topsoil and garden soil?
Topsoil is the natural upper layer of soil from the ground. It contains mineral particles, organic matter, and the microorganism life that plants need. Garden soil is a processed blend, typically topsoil plus compost or other amendments, sold in bags at hardware stores. Bagged garden soil is more consistent and weed-free than bulk topsoil, but much more expensive per cubic yard.
How long after adding topsoil should I wait to seed?
You can seed immediately after spreading and raking topsoil level. Watering it in settles the surface and helps seed-to-soil contact. What you cannot do is seed on newly placed, loose topsoil that has not been raked and tamped smooth, since the uneven surface prevents good germination. Time it so you seed at least 6 weeks before the first frost in fall, or in spring once the soil temperature hits 50 degrees.
Is topsoil or compost better for lawns?
Use topsoil for filling low spots, leveling, and establishing new lawn areas. Use compost for improving existing lawn soil: spread a half inch of compost over an established lawn and rake it into the grass to feed the soil biology without smothering the turf. For new seeding in areas where the soil depth is inadequate, add topsoil first to reach the right depth, then apply a thin layer of compost on top before seeding.
How many bags of topsoil equal a cubic yard?
A standard 40 lb bag of topsoil holds about 0.75 cubic feet. One cubic yard equals 27 cubic feet, so you need 27 divided by 0.75, or about 36 bags per cubic yard. At $5 to $7 per bag, that adds up to $180 to $250 per cubic yard from bags, versus $25 to $55 per cubic yard for bulk topsoil. For anything over 3 cubic yards, bulk delivery saves money even after the delivery fee.
Use the topsoil calculator to get exact cubic yards, bag count, and cost estimate for your project. For raised garden beds specifically, the topsoil calculator for raised beds handles different depth and dimension inputs, and shows how much per bed.