The Two Piles Look The Same, But They Do Opposite Jobs
A dump truck backs up your driveway, tips the bed, and leaves a brown pile on the tarp. Fill dirt and topsoil arrive looking close enough that plenty of homeowners cannot tell which one they got until they start spreading it. That is the whole problem with this purchase. The two materials cost different money, weigh differently, and do jobs that are close to opposite, but the ordering decision happens in a moment when they seem interchangeable.
The most common version of the mistake goes like this. Someone has a dip in the back lawn that collects water and scalps every time the mower crosses it. They order a few yards of topsoil, rake it in, seed it, and it looks great by midsummer. Eighteen months later the dip is back. Nothing went wrong with the work. The wrong material went in the hole.
What fill dirt actually is
Fill dirt is subsoil that comes out of local excavation work, screened to pull out debris. It sits below the layer where roots and organic life live, so it is low in organic matter and heavier on clay, sand, and mineral content. That composition is not a defect. It is the point. Because there is little organic material in it, there is little in it that can break down and disappear. It stays where you put it.
Think of fill dirt as a structural material rather than a growing medium. It is what you use to raise low ground, backfill around a foundation or a pool, and build the base up before topsoil goes on. It runs 1.3 tons per cubic yard, which means even a modest order is genuinely heavy. Give some thought to where the truck can drop it and how far you are willing to push a wheelbarrow, because that distance is the part of the job people underestimate.
To turn your measurements into an order, our topsoil calculator works out the cubic yards from the area and depth.
On price, fill dirt sits in a low band relative to topsoil. That gap barely registers on a single yard. Once you are moving eight or ten yards, it is the reason layering makes sense financially instead of just technically.
What topsoil actually is
Topsoil is the surface layer, the one where organic matter, roots, and soil life are concentrated. It holds moisture, it feeds seedlings, it is what grass actually wants to root into. Screened topsoil has had rocks, sticks, roots, and clumps pulled out of it so it rakes smooth and seeds evenly.
The same organic matter that makes topsoil good at growing things also makes it a poor structural fill. Organic matter decomposes. As it does, the material loses volume. A thin layer of topsoil losing a fraction of its volume is invisible. A thick layer of topsoil losing that same fraction is a dip returning to your lawn.
Key takeaway: choose fill dirt when the job is raising ground and topsoil when the job is growing grass. Most real low spots need both, in that order, bottom to top.
How Deep Is Your Low Spot? That Decides What You Buy
Depth is the deciding variable, not the size of the area and not what the spot looks like after a rain. Measure before you order anything.
Shallow dips, roughly two to three inches or less, are a topsoil job and nothing more. Screened topsoil raked into the depression, blended out at the edges, seeded over, kept watered. There is no structural work happening at that depth and no reason to complicate it.
Past that, a topsoil-only fill starts to punish you. The deeper the layer, the more total volume is tied up in material that shrinks as it breaks down. This is the failure mode people describe as the lawn settling again, and it commonly shows up within a year or two of the repair.
Deeper depressions belong to fill dirt with a topsoil cap. That covers the sunken area alongside a foundation, the soft circle where a stump used to be, and the long shallow trench line that appeared over a utility run after a few wet seasons. Typical install depth for fill dirt runs 6 to 12 inches, which lines up neatly with what most residential low spots actually measure once you check them properly.
Here is the field check worth doing. Lay a straight board or run a string line taut across the dip, resting on undisturbed ground at both ends, then measure straight down to the surface at several points along it. Do it in two directions if the spot is wide. You want the low point and a sense of how the depth varies, because that measurement is what you order against. Eyeballing a dip almost always underestimates it.
One caveat before you spend a dollar on material. If the spot holds water because of where runoff travels, filling it relocates the puddle rather than fixing it. Walk uphill from the low spot during or right after a rain. Look at where downspouts discharge, whether the grade genuinely falls away from the house, and whether a driveway or patio edge is aiming water at that one place. Fix the source first, then fill.
The Layered Fix: Fill Dirt Below, Topsoil On Top
The sequence matters as much as the materials. Done in order, this is a repair that stays repaired.
Start with what is already there. If the existing sod is healthy and the spot is small, cut it out in manageable squares with a flat spade and set it aside on a tarp in the shade, grass side up, kept damp. If you are not saving it, at minimum slice through it heavily in a grid so the new material bonds to the ground underneath instead of sitting on a mat of thatch. Burying live turf under several inches of soil leaves a soft decomposing layer that sinks unevenly and shows up later as a lumpy patch.
Placing fill dirt in lifts
Place fill dirt in 6 to 8 inch lifts and compact each lift before the next one goes in. This is the single instruction people skip, and skipping it is why filled areas keep sinking for years afterward. A deep pile of loose dirt is mostly air. That air leaves eventually, on its own schedule, usually after you have seeded.
For compaction, a hand tamper is enough for a spot a few feet across. For anything larger, rent a plate compactor for a half day. Water each lift lightly before tamping, since slightly damp material compacts far better than bone dry material. Do not soak it. Saturated clay smears and pushes around rather than tightening up.
Stop the fill dirt several inches below your finished grade. You need that room for the cap, and it is easier to plan for than to correct later.
How much topsoil goes on top
Cap with screened topsoil anywhere grass or plants need to grow. Grass roots need real soil with organic matter in it, so this layer should be deep enough to root into rather than a dusting over subsoil. Four to six inches is a reasonable working depth for turf.
Rake the topsoil so it blends into the surrounding lawn rather than stopping at a hard edge. You want water to run across the repaired area, not collect at a seam. Feather the last foot or so out into the existing grass.
Then seed or sod, and keep it watered. If you saved the original sod, lay it back over the fresh topsoil, butt the pieces tight, and press them down so roots make contact. This cut and patch approach works well for small spots and skips the waiting and weeding that comes with seeding.
Running The Yardage: Two Examples Worth Copying
The formula
Length in feet times width in feet times depth in feet, divided by 27. Depth is almost always given in inches, so divide inches by 12 first to get feet.
Our coverage rule for fill dirt gives you a quick sanity check on the answer. One cubic yard covers about 54 square feet at 6 inches deep.
Example one, the fill dirt base. Say the sunken area measures 20 feet by 20 feet and you need 6 inches of fill. That is 400 square feet. Six inches is 0.5 feet, so 20 times 20 times 0.5 equals 200 cubic feet, and 200 divided by 27 is about 7.4 cubic yards. Check it against the coverage rule. 400 square feet divided by 54 square feet per yard is also about 7.4. The two methods agree.
Adding a settling buffer
That 7.4 yard figure is loose material. Once it is placed in lifts and compacted, it occupies less space than it did in the pile, so the loose number always understates what you need. Add roughly 15 percent to fill dirt for compaction and settling. 7.4 plus 15 percent is about 8.5 cubic yards. Order 8.5.
Example two, the topsoil cap. Same 20 by 20 area, 4 inches of topsoil on top. Four inches is 0.333 feet, so 20 times 20 times 0.333 equals about 133 cubic feet, and 133 divided by 27 is about 4.9 cubic yards. Round up rather than down. Running a wheelbarrow short at the far edge of a project is a worse outcome than having a little extra to spread elsewhere.
Now the weight side of that math. At 1.3 tons per cubic yard, an 8.5 yard fill dirt order comes to roughly 11 tons. That is the number that settles the bagged versus bulk question on its own. No amount of trailer trips is a sensible way to move that, and bulk delivery is meaningfully cheaper per yard besides.
For an odd-shaped depression, break it into two or three rectangles, measure the depth at several points inside each rectangle, average those depths, and run the formula on each piece before adding the results. A volume calculator handles the arithmetic if you would rather not, but you still have to do the measuring honestly.
How Much Settling To Actually Expect
Two different things get called settling, and they behave differently.
Fill dirt settles mechanically. Air voids between particles close up under weight, rain, and time. Compacted in lifts, it drops a little early on and then essentially stops. Dumped in loose, it keeps moving through wet and dry cycles for years, which is the version homeowners notice and complain about.
Topsoil shrinks chemically, if you like. The organic matter in it decomposes and that volume is gone for good. This is the argument against filling a deep hole with topsoil alone. Eight to ten inches of pure topsoil in a deep depression will very likely sink again within a year or two, no matter how carefully you raked it.
Set expectations for the first season even on a properly layered repair. Expect a small amount of drop, most of it showing up after the first few heavy rains, and plan on topdressing once with a bit more topsoil to bring it back flush. That is normal, not a sign the job failed.
Two habits make the difference. Overfill a compacted area slightly, crowning it just above the surrounding grade so it settles down to level instead of settling into a fresh dip. And do the work when the soil is workable rather than saturated. Wet clay smears under a tamper instead of compacting, and it will not hold the grade you set.
Common Mistakes That Turn Into A Soggy Patch
- Dumping fill on live grass. Buried turf rots into a soft layer that compresses unevenly. Cut the sod out or score through it heavily first.
- Filling in one deep lift. This is the most common single reason a repaired area sinks again. Six to eight inch lifts, compacted individually, every time.
- Seeding straight into fill dirt. It is low in organic matter and often clay heavy. Seed germinates thin, roots stay shallow, and the patch stays a different color and texture than the rest of the lawn all summer.
- Building grade toward the house. If you are filling near a foundation, the finished surface has to fall away from the structure. Fill dirt is the right material there, but only if the slope goes the right direction.
- Buying unscreened fill. Rocks, chunks, and construction debris make a mess of compaction and turn up in the lawn for years. Ask for clean, screened material.
- Ignoring why the dip exists. A settled trench over an old utility line, a downspout discharging in one spot, or a leaking irrigation line will recreate the depression regardless of what you fill it with.
- Confusing a leveling mix with fill. Sand and topsoil blends are meant for topdressing thin surface irregularities. They are not a material for raising ground several inches.
How We Started
We started Mulch Mound because we got tired of the hassle that came with buying landscaping materials. The options were either loading bags into your car at a garden center or calling around to local suppliers, trying to figure out pricing, minimums, and delivery schedules. Neither option felt convenient or transparent.
Three of us – Alec, Mo, and Tyler – decided there had to be a better way. Alec and Tyler got their start back in 2013 running a landscaping business during college, moving mulch and mowing lawns to pay tuition. That experience taught them how frustrating it was to source materials, and years later, that frustration turned into Mulch Mound.
We focus on making it simple to get mulch, stone, and soil delivered directly to your home. Order online, pick your delivery date, and we handle the rest. No loading bags. No calling multiple suppliers. No wondering if you bought enough or paid a fair price.
We work with quality local suppliers in the areas we serve and aim to be straightforward about what we offer and what it costs. Landscaping is hard work. Buying the materials for it shouldn't be.
Frequently asked questions
Do I have to remove the existing grass before filling a low area?
It depends entirely on how much material is going on top. For a shallow topdressing of an inch or so, no. Work fine soil down between the blades with the back of a rake and let the grass grow up through it, spreading it over two or three applications a few weeks apart rather than smothering the lawn in one go.
For anything you are burying under several inches, slice the sod out with a flat spade or at least score it heavily in both directions. You do not want to build a repair on a mat of living turf that is about to rot.
Can grass grow directly in fill dirt?
Sometimes something comes up, but it will be thin and it will suffer the first time the weather turns dry. There is little organic matter in fill dirt to hold moisture, and clay heavy subsoil compacts hard enough that shallow roots have trouble getting anywhere.
If you inherited a yard of bare fill dirt from a builder or a contractor, the answer is not more seed and more fertilizer. It is adding a real topsoil layer over the top, deep enough to root into, and starting from there.
How much does a yard of topsoil weigh?
Topsoil weight moves a lot with moisture content, and soaked soil is dramatically heavier than dry. That is why the honest answer is a range rather than a figure. For a useful comparison, our fill dirt runs 1.3 tons per cubic yard.
The practical version of this question is usually about hauling. Whatever the exact weight, a half ton pickup bed is not the right tool for multiple yards of either material. Payload capacity runs out well before bed volume does.
Is fill dirt or topsoil cheaper delivered?
Fill dirt sits in a lower price band than topsoil, and that gap is a real part of why layering makes sense. You are buying the inexpensive structural material for the bulk of the volume and paying the higher price only for the top few inches where it actually earns its keep.
Run it against the 20 by 20 example. Roughly 8.5 yards of the cheaper material underneath and about 5 yards of the more expensive material on top costs less than 13 or 14 yards of topsoil, and it produces a repair that holds its grade instead of sinking.
When is the best time of year to do this?
Any time you can get seed or sod established afterward and the ground is neither saturated nor frozen. The seeding window for your grass type is the real constraint, since bare soil sitting exposed through a wet stretch just erodes.
Avoid working saturated clay in particular. It will not compact properly, it smears under a tamper, and you will be redoing the grade once it dries out.