Topsoil Calculator: How Much Soil Do You Need?

I Ordered Way Too Much Topsoil Once

I'm talking about a full dump truck load — something like 10 cubic yards — for a backyard garden bed that honestly needed maybe 3. The driver backed in, dumped it, and I just stood there looking at this mountain of dirt thinking, "well, that's a problem." I spent the next two weekends wheelbarrowing the excess to neighbors who didn't even ask for it. And the thing is, the math to figure out how much I actually needed? It's not hard. I just didn't do it.

So yeah, that's why I'm kind of passionate about this particular calculation.

If you're putting in a new lawn, filling raised beds, leveling out a yard, or topping off garden areas, you need to know how many cubic yards of topsoil to order. Not a rough guess. An actual number. Because topsoil isn't cheap — we're talking somewhere in the ballpark of 25 to 50 per cubic yard depending on where you live and the quality — and ordering too much or too little is annoying either way.

The Math Behind It (It's Honestly Just Multiplication)

Here's the deal. Topsoil gets sold by the cubic yard. Your garden bed or lawn area is measured in feet. So you need to convert, and that's where people trip up.

💡 THE FORMULA

Cubic Yards = (Length in feet × Width in feet × Depth in inches ÷ 12) ÷ 27

Length = how long the area is (feet)
Width = how wide the area is (feet)
Depth = how thick you want the topsoil layer (inches, divided by 12 to convert to feet)
27 = number of cubic feet in one cubic yard

That division by 12 is because you're converting your depth from inches to feet. And the division by 27 is because there are 27 cubic feet in a cubic yard (3 × 3 × 3). I had no idea where that 27 came from the first time someone told me — I just nodded. But it's literally just 3 feet cubed.

Let me walk through a real example.

Say you've got a rectangular garden bed that's 20 feet long and 10 feet wide, and you want to add 4 inches of topsoil on top. Here's how that breaks down:

1. Convert the depth: 4 inches ÷ 12 = 0.333 feet

2. Multiply everything: 20 × 10 × 0.333 = 66.6 cubic feet

3. Convert to cubic yards: 66.6 ÷ 27 = about 2.47 cubic yards

So you'd order roughly 2.5 cubic yards. Most suppliers will round to the nearest half yard anyway, which works out perfectly here. I'd probably order 3 just to have a tiny buffer, but that's me being cautious after the Great Topsoil Mountain Incident of 2019.

If your area isn't a perfect rectangle (and honestly, whose yard is?), you can break it into smaller rectangles or use our topsoil calculator to handle irregular shapes. For circular beds, you'd swap length × width for π × radius², but that's a whole other thing — our circle calculator can help with that part.

Quick Reference: Common Topsoil Amounts

I put this table together because these are the scenarios I run into most often. It assumes a 4-inch depth, which is pretty standard for most garden and lawn projects.

That weight column is based on topsoil weighing roughly 2,000 lbs per cubic yard, give or take. Wet topsoil is heavier — sometimes significantly so. That's worth knowing if you're picking it up yourself in a truck bed, because a half-ton pickup maxes out around 1,000 to 2,000 lbs of payload. One cubic yard of wet topsoil could push that limit real fast.

That's a lot of dirt!

How Deep Should You Actually Go?

This depends entirely on what you're doing with it.

For new lawns, most people go with 4 to 6 inches. Grass roots need room to establish, and if you skimp on depth you'll end up with thin, patchy turf that dies the first time it gets hot. I've seen people lay sod over 2 inches of topsoil and wonder why it turned brown in August. The roots had nowhere to go.

For garden beds — especially vegetable gardens — you want more like 6 to 12 inches, depending on what's underneath. If you're building raised beds on top of concrete or compacted clay, go deeper. If you're amending existing decent soil, 4 inches might be plenty. For just topping off an existing lawn that's gotten a little thin or uneven, even 1 to 2 inches can do the trick (and that's called topdressing, which is basically just a light refresh).

The mulch calculator uses the same basic formula if you're also planning to add mulch on top — same length × width × depth logic, just a different material. And if you're working on a bigger landscaping project that involves concrete or gravel, our concrete calculator and gravel calculator work the same way too.

A Few Things I Wish Someone Had Told Me

Topsoil settles. Like, a lot. Freshly delivered topsoil that you spread to 4 inches will compact down to maybe 3 or 3.5 inches after a few weeks of rain and gravity doing their thing. So ordering an extra 10-15% isn't being wasteful — it's being realistic. You can use a percentage calculator to figure out that buffer quickly.

Also, not all topsoil is the same. Some places sell "topsoil" that's basically subsoil with some organic matter mixed in. If it looks gray and clumpy, that's not great. Good topsoil should be dark, crumbly, and smell like earth (not sulfur, not nothing). Ask your supplier what's in it.

And measure twice. Seriously.

I've started measuring my areas with a tape measure and then double-checking with a phone app, because I once measured a bed as 15 feet when it was actually closer to 12 and ended up with — you guessed it — too much soil again. If you're working with area measurements and need to convert between units, our area calculator is handy, and the length converter helps if you're bouncing between meters and feet.

For bigger landscaping projects where you're also budgeting labor and materials, you might find our salary to hourly converter useful if you're hiring help by the hour and trying to figure out total cost.

Can I use regular dirt instead of topsoil?

You can, but you probably shouldn't. Regular dirt from your yard (subsoil) is usually compacted, nutrient-poor, and full of clay or rocks. Topsoil is specifically the top layer of earth — the part with organic matter, microorganisms, and the nutrients plants actually need. Mixing some existing soil with purchased topsoil is fine, but replacing topsoil entirely with whatever's in the ground already is a recipe for sad plants.

How many bags of topsoil equal a cubic yard?

Roughly 36 bags if they're the standard 0.75 cubic foot size. That adds up fast — and gets expensive. Bagged topsoil usually runs 3 to 7 per bag, so 36 bags could cost you 108 to 252 for a single cubic yard. Bulk delivery is almost always cheaper if you need more than about 2 cubic yards.

Does topsoil need to be compacted after spreading?

Lightly, yes. You don't want to pack it down hard — that defeats the purpose of having loose, airy soil for roots. But a gentle tamping or just watering it well and letting it settle naturally for a few days is a good idea before planting or laying sod.