Fill dirt vs topsoil: what is the difference?
The most common question in this trade and the one that costs the most money when it goes wrong. Fill dirt and topsoil are 2 different layers of the same ground, they cost different amounts per cubic yard, and most grading jobs need both. Here is the difference in 1 paragraph and 1 table.
What is the difference in one paragraph?
Fill dirt is subsoil. Topsoil is the layer above it. Fill dirt is the mineral ground under the organic surface layer, mostly clay, silt and sand, bought for volume. Topsoil is the organic surface layer, bought for growing. Fill is cheaper, heavier and more stable. Topsoil settles. Most jobs want both: fill for the lift, 4 to 6 inches of topsoil on top.
Fill dirt and topsoil, head to head
The comparison in full. Any figure here moves with moisture content and with the ground the material came off, so use them for planning and confirm anything your engineer has specified.
| Fill dirt | Topsoil | |
|---|---|---|
| Where it sits in the ground | Below the organic layer | The top few inches |
| Organic content | Minimal to none | This is what defines it |
| What it is bought for | Volume, grade, mass | Growing grass, sod and plants |
| Behaviour over time | Stays put once placed and dried | Consolidates, settles, loses volume |
| Under a slab or driveway | Only select fill, never clay fill alone | Never |
| In a garden bed | As bulk underneath only | Yes, as the growing layer |
| Typical depth placed | In lifts to any height you need | 4 to 6 inches lawn, 8 to 12 inches beds |
| Cost per cubic yard | The cheapest bulk material sold | Typically the dearest |
| Weight per cubic yard | Heavier, heavier again when wet | Lighter, easier to move by hand |
| Moving 20 cubic yards | Get a skid steer or a tractor | 9 to 14 wheelbarrow loads per yard |
Why does using the wrong one cost so much?
The mistake runs in both directions and both are expensive. Filling a hole with topsoil means paying the dearest material on the list for a job the cheapest one does better, and then watching the ground sink as the organic content breaks down. Capping a new lawn with fill dirt means paying for material that will not grow grass, then paying again for the topsoil you should have ordered.
Bulk material does not get returned. Once a load is tipped on your ground the trucking has been spent, and trucking is roughly 90 percent of what a cubic yard of dirt costs. There is no undo, and a corrective order is a full trucking charge on a small quantity, which is the worst price per yard available anywhere.
The cost of getting it right is 1 phone call. Describe the job, the depth and whether anything has to grow, and the answer takes about 2 minutes.
What combination do most jobs actually want?
Build the grade with clay fill dirt. Cap it with topsoil. That is the answer for raising a low back yard, for levelling a lot before sod goes down, for repairing a washed-out area, and for most of the residential grading work we deliver into across every market.
The usual split is everything but the top 4 to 6 inches in fill, and the top 4 to 6 inches in topsoil. On a 1,000 square foot area raised by 1 foot, that is roughly 25 cubic yards of fill and 12 cubic yards of topsoil, for about 37 cubic yards total. Run your own numbers rather than taking those as gospel, because the split changes sharply with how deep you are going. At 6 inches total depth almost all of it is topsoil. At 3 feet almost none of it is.
Sequence matters as much as the split. The fill goes down first and gets shaped and settled. The topsoil arrives once the grade underneath is right. Order both on the same day and you will move the topsoil twice.
Where does select fill sit between them?
There is a third material this comparison usually misses, and in our 2 Texas metros it is the one that matters most. Select fill is not a grade of fill dirt. It is a different product, chosen for its gradation so that it compacts to a predictable density under a plate compactor or a roller.
If what you are filling will eventually carry a slab, a driveway, a patio or a footing, neither of the 2 materials on this page is the right answer. You want select fill placed in 6 to 8 inch lifts and compacted lift by lift, usually to 95 percent of a Proctor maximum dry density. Clay fill under a structure swells and shrinks with the seasons, and that movement is the mechanism behind most residential foundation damage across the Blackland Prairie and the Gulf Coast clays.
In Colorado the same material is called structural fill. In California plans it is engineered fill or import fill. Different words, same job.
How do I tell them apart on site?
Colour is the first tell and not a reliable one. Topsoil in our markets tends to run darker, finer and more powdery, and it crumbles in your hand. Clay fill runs chunkier, holds together in a ball when it is damp, and dries hard. Select fill often has a reddish cast in Texas and a visibly more granular, sandy feel than clay fill.
The reliable test is what happens when it dries. Clay fill sets up hard and holds its shape, which is why motocross tracks and pond berms are built out of it. Topsoil stays loose and friable when it dries, because that is what a root system needs. If a pile dries into something you could shape a jump face out of, it is not topsoil.
The second test is the smell and the life in it. Topsoil smells like soil and has visible organic matter, roots and occasionally worms through it. Fill dirt smells like nothing and has almost no life in it, which is exactly why nothing grows in it.
Where do I go from here?
Work out the total volume first, then split it by depth. The calculator takes length, width and depth and returns cubic yards with an allowance for settlement, so you can run it twice: once for the full lift in fill and once for the top 4 to 6 inches in topsoil. Then we need the delivery address to price it.
Fill dirt and topsoil questions
Is fill dirt cheaper than topsoil?
Yes, usually by a wide margin. Fill dirt is abundant, it sits under every construction site in the country, and it needs almost no processing. Topsoil is a thin surface layer, it is finite, and every cubic yard sold came off the top of somewhere else. Scarcity is the reason for the price gap, not processing cost.
Will grass grow in fill dirt?
Not well and not for long. There is close to nothing in fill dirt for a plant to live on. Grass seeded directly into clay fill will struggle in the first dry spell because the roots hit dead, dense ground. If grass has to grow, put 4 to 6 inches of topsoil over the fill first.
Can I just put topsoil on top of the old lawn?
Only in thin layers. Top-dressing at a quarter to half an inch per pass works and is how low spots get smoothed out over a couple of seasons. Burying living turf under several inches of soil smothers it and leaves a layer of decomposing grass under your new grade. To raise a lawn significantly, strip or kill the grass first, build the grade, then re-sod or re-seed.
What is another name for fill dirt?
Common fill, general fill, or just fill. In some markets you will also hear it called clay fill. They all describe the same material: the mineral subsoil under the organic layer. Select fill is not a synonym for any of these. It is a separate spec-driven product and it costs more.
Which one fills in a swimming pool?
Clay fill dirt for the volume, which is almost all of it. The shell gets broken up so water drains through instead of collecting in a bathtub, then the hole is backfilled with common fill in lifts. Topsoil goes on only at the very top, 4 to 6 inches of it, if grass is going over it afterwards. Budget 60 to 100 cubic yards for a typical residential pool.
Is fill dirt or topsoil better for levelling a yard?
Both, in that order. Use clay fill to build the grade up to where you want it, then cap the whole area with 4 to 6 inches of topsoil so grass will grow. Using topsoil for the whole lift is the most expensive way to do it and the result sinks. Using fill for the whole lift is cheaper and nothing grows on it.
Most jobs want both
Build the grade with clay fill and cap it with four to six inches of topsoil. Tell us the area and the depth and we will work out the split with you.