Whether you're starting a new lawn, planting a vegetable garden, or filling raised beds, the wrong amount of topsoil can sink your entire project. Too little and your plants won't have enough nutrients to thrive. Too much and you're wasting money. But how much do you actually need?
The good news: figuring it out is easier than you think. You don't need to guess, and you don't need a degree in landscaping. In this guide, we'll walk you through exactly how much topsoil you need—plus a simple formula (or calculator) to do the math for you.
What is Topsoil, Anyway?
Topsoil is the nutrient-rich upper layer of soil that plants actually want to grow in. It's darker, looser, and packed with organic matter—unlike the dense subsoil underneath. When you order topsoil for delivery, you're getting the good stuff that makes gardens and lawns thrive.
How Much Topsoil Do You Need? The Formula
Here's the basic formula:
Length (ft) × Width (ft) × Depth (inches) ÷ 324 = Cubic Yards
Wait, where did 324 come from? Here's the math:
- 1 cubic yard = 27 cubic feet
- 27 cubic feet × 12 inches per foot = 324 cubic inches per cubic yard
Example 1: Lawn Area
You want to spread topsoil across a 20' × 30' lawn, 2 inches deep.
20 × 30 × 2 ÷ 324 = 3.7 cubic yards
You'd order 4 cubic yards (accounts for settling).
Example 2: Raised Beds
You have a 4' × 8' raised bed, and you want to fill it 12 inches deep.
4 × 8 × 12 ÷ 324 = 1.18 cubic yards
You'd order about 1.5 cubic yards (accounts for settling).
Example 3: Multiple Areas
You're doing:
- 500 sq ft lawn at 2" deep = 3.1 cy
- 3 raised beds (4×8 each) at 12" deep = 3.5 cy
- 100 sq ft flower bed at 4" deep = 1.2 cy
Total = 7.8 cubic yards → order 8 cy
How Deep Should Your Topsoil Be?
It depends on what you're growing:
| Project | Depth | Why |
|---|---|---|
| Lawn seeding | 2-3" | Enough for grass roots to establish |
| Lawn renovation | 3-4" | Covers uneven ground |
| Flower beds | 4-6" | Deep for shrubs and perennials |
| Vegetable gardens | 8-12" | Deep for root vegetables |
| Raised beds | 10-12" | Full depth needed |
| Trees & shrubs | 12"+ | Deepest rooting needs |
Raised Bed Topsoil Quick Reference
Can't do math in your head? Use this quick reference:
| Bed Size | 8" Deep | 10" Deep | 12" Deep |
|---|---|---|---|
| 2×4 | 0.24 cy | 0.3 cy | 0.36 cy |
| 4×4 | 0.48 cy | 0.6 cy | 0.73 cy |
| 4×8 | 0.97 cy | 1.2 cy | 1.46 cy |
| 4×12 | 1.45 cy | 1.8 cy | 2.2 cy |
Round up 0.5+ to next whole number
Real-World Tips
- Always round up. Soil settles, and you'd rather have extra than run short.
- Account for settling. New topsoil typically settles 10-15% in the first season.
- Mix if you can. Topsoil + compost (50/50 or 60/40) is even better than pure topsoil.
- Don't skimp on depth. Thin topsoil means shallow roots, which means stressed plants.
Harbor Soils Topsoil Delivery
If you're in Gig Harbor, Port Orchard, Silverdale, Bremerton, Purdy, Artondale, or Olalla, you can order bulk topsoil delivery with no minimums and same-day service.
Use our topsoil calculator above, then call 253-857-5125 to order. We'll deliver exactly what you need.
Last updated: March 5, 2026
Frequently Asked Questions
Can I just buy bagged topsoil instead of having it delivered?
For projects under 1 cubic yard (about 13 bags of 2-cu-ft topsoil), bagged is fine and avoids the delivery fee. For anything over 1.5 yards, bulk delivery is dramatically cheaper. A typical 2-yard project costs $200+ in bags but roughly $66 to $92 in bulk plus delivery from Harbor Soils 3-Way Topsoil Mix.
Do I need to till topsoil into the existing soil?
For lawn topdressing (1/2 inch or less), no. For new garden beds, yes. Tilling 4 to 6 inches of topsoil into the top 4 inches of native soil creates a transition layer roots can grow through. Dropping a thick topsoil layer onto compacted clay without integration creates a perched water table; roots stay shallow and plants struggle.
What's the difference between topsoil and garden soil for my project?
Plain topsoil is screened mineral soil. Garden Mix (Mushroom Compost Blend) is topsoil pre-blended with compost. For filling and grading, plain topsoil is the right call. For new vegetable beds or planting in the same week, the Garden Mix saves you the step of amending separately.
How much extra topsoil should I order for a brand-new lawn?
Add 15 percent to your calculated need. New lawn projects almost always reveal hidden low spots once you start spreading, and grade settles unevenly during the first watering. Better to have an extra wheelbarrow's worth than to need a second delivery.
How long can topsoil sit in a pile before I have to use it?
Indefinitely if covered with a tarp. Even uncovered, quality holds up for months. Long sun exposure dries the surface; long rain saturates and adds weight. If you can't spread for a week or more, tarp it.
Why do vegetable gardens need 8 to 12 inches of topsoil?
Most vegetables develop their feeder roots in the top 6 inches and their deeper roots down to 12. Carrots, parsnips, and other root crops specifically need that full depth for proper formation. If your native soil under the topsoil is heavy clay or compacted till (typical in Kitsap), the topsoil layer essentially becomes your entire root zone.