Multiply the pad's length, width, and average fill depth in feet, divide by 27 to get cubic yards, then add 15 to 25 percent because loose dirt shrinks when it's compacted. A 40 by 60 foot pad built up 2 feet works out to about 178 cubic yards in the ground, which means ordering roughly 205 to 220 yards delivered.
That's the quick answer. The part that moves the number is what your engineer or building department calls for, and whether you can cut high ground on the same lot instead of buying dirt. Here's how we run the math at Walberg, Inc. when a Tehama or Butte County owner asks us for a house pad.
The basic fill dirt formula
Fill is sold by the cubic yard, and a cubic yard is 27 cubic feet. So:
Length (ft) x Width (ft) x Average depth (ft) / 27 = cubic yards in place
Use the average depth, not the deepest spot. On a sloped lot the pad is deep on the downhill side and zero on the uphill side, so the average might be half of the tallest point. Walk the corners, note the finished pad elevation against existing grade at each one, and average them.
Here's what that looks like on a few common pad sizes, before any compaction allowance:
| Pad size | Average fill depth | Cubic yards in place |
|---|---|---|
| 30 x 40 ft | 1 ft | about 44 |
| 40 x 60 ft | 2 ft | about 178 |
| 50 x 80 ft | 3 ft | about 444 |
Don't forget the shoulders. A pad needs a building footprint plus room around it for the slope, so the fill area is bigger than the slab. A 2 to 1 side slope on a 3 foot pad adds 6 feet on every side, and people forget that every time.
Why you order more than the math says
Dirt that's been dug and trucked is fluffy. Once it's spread in lifts and compacted, it settles into a smaller volume. Supplier guides commonly suggest adding 10 to 25 percent, and for a pad that will carry a house we'd plan on the high end of that range.
So the 178 yard pad above becomes about 205 yards at 15 percent and about 222 yards at 25 percent. If the soil is dry and clean you may land at the low end. If it's wet clay you'll lose more to shrink, and you'll fight the moisture content too.
Two things we'd tell any owner here:
- Your soils report sets the real compaction target, often 90 or 95 percent of maximum dry density, so read it before you order.
- Order a little long. A short load that arrives after the grader has left costs more than 10 extra yards sitting in a pile.
Our post on house pad compaction testing covers what the tests look like and who pays for retests.
Do you need to import dirt at all?
Often not. A lot of Northern California building sites have a high corner or a driveway cut that produces more dirt than the pad needs. That's called balancing cut and fill, and it's the cheapest dirt you'll ever get because it's already on the property.
Here's where it breaks down. If the native soil is full of rock, roots, or organic topsoil, it can't go under a slab as structural fill. We can often run it through a screen and recover the clean fraction. That's what dirt screening is for, and it can cut the amount of import you buy.
On the other hand, if the site is flat and the pad only needs a foot of lift, the cut is too small to matter and you'll haul in all of it. We'd rather tell you that up front than have you count on dirt that isn't there.
What affects the delivered price
We won't quote a per-yard number in a blog post because it changes with the source pit, the haul distance, and the season. Here's what drives it:
- Haul distance from the pit or yard to your gate. A rural lot off a county road costs more to reach than one near Corning or Chico.
- Material type. Plain fill, engineered structural fill, and recycled base from a concrete yard are priced differently. Our concrete and asphalt recycling yard can be a source for some applications.
- Access. A wet driveway that can't carry a loaded truck adds days.
- Weather. Dirt that's soaked in November takes longer to dry and place than the same dirt in July.
For a full picture of pad pricing, including excavation, spreading, and testing, see our house pad cost guide and the house pads and driveways page.
Timing the delivery
In the Sacramento Valley the wet season runs roughly November through March. We'd wait for a dry stretch before we cut and place structural fill, because mud under a slab turns into cracks two winters later. If the pad has to go in now, expect to disc and dry the lifts, and expect some days to be lost to rain.
If the disturbed area is an acre or more, you'll also need construction stormwater coverage under the State Water Board's construction general permit, plus a plan for keeping dirt out of the ditch. Check your county grading rules too. Our grading page and the Tehama County grading permit post list what to ask for.
Common Questions
How many cubic yards of fill dirt do I need for a 30 by 40 pad?
At 1 foot of average depth you need about 44 cubic yards in place. With a 15 to 25 percent compaction allowance, order about 50 to 55 yards. Add more if the side slopes extend beyond the 30 by 40 footprint.
How many tons is a yard of fill dirt?
Most fill dirt weighs about 1.2 to 1.4 tons per cubic yard, depending on moisture. A 200 yard pad therefore moves roughly 240 to 280 tons. Suppliers who sell by weight will give you a different number than suppliers who sell by volume, so ask which one the quote uses.
Does fill dirt have to be compacted for a house pad?
Yes. Structural fill under a slab or footing is placed in thin lifts and compacted to the percentage in your soils report, and a testing lab usually verifies it. Uncompacted fill settles unevenly, and that's how slabs and garage floors crack.
Can I use dirt from my own property?
Sometimes. Clean native soil without roots, trash, or organic topsoil can usually be reused, and screening can recover usable material from dirtier soil. Your engineer decides what qualifies as structural fill.
The bottom line
Run the length, width, and depth math, add at least 15 percent, and get the compaction spec from your soils report before you buy a single load. Then check whether a cut on your own lot can cover part of it. If you'd rather have someone walk the site and give you a real number, request a free estimate from Walberg, Inc. and we'll tell you what the pad needs and what it doesn't. You can also check any hauler's license on the CSLB site before you hire.