Site work is where estimates go wrong in ways nobody can see on the drawings. The building is drawn in detail. The ground under it is described by a handful of borings and a topo survey. Rock, soft clay, groundwater, buried foundations and unmarked utilities all show up after the bid, and they show up in the site package.
This guide covers how to build a site work estimate from quantities and unit prices, where to find published unit prices you can check against, the cut and fill mistakes that cost the most, and how to structure contingency and contract terms around what you can't see.
Why Site Work Is Hard to Price
Other trades bid from complete drawings. Site work bids from a model of the subsurface built on a few data points. The geotechnical report might have one boring for every large area of the site, and everything between borings is interpolation. That uncertainty is the core problem, and every technique in this guide is a way to measure it, price it, or move it to the party best able to carry it.
The underground conditions that cause most trouble:
- Rock. Ripping or drilling and blasting costs far more per yard than common excavation, especially in confined areas.
- Unsuitable soils. Soft clay, organics or wet material under a pad must be undercut, hauled off and replaced with structural fill.
- Groundwater. Dewatering adds equipment and pumping time, and wet soils are harder to compact.
- Buried debris. Old foundations, slabs, tanks and fill on previously developed sites.
- Utility conflicts. Existing lines that are mislocated or not shown.
Borings are cheap compared with surprises
The geotechnical report is the most important document in the site package. Read the boring logs, not just the summary: depth to rock, groundwater readings, soil classifications, and the engineer's recommendations for undercut and fill. Note where borings are missing, such as under detention ponds, deep utility runs, and the deepest cuts. Where coverage is thin, say so in your bid and either price the risk or carry unit prices for it.
Published Unit Prices You Can Check Against
Private site contractors don't publish prices, but state DOTs publish weighted average bid prices for every pay item they let. These are highway prices on large quantities, so treat them as a floor for big open work, not a quote for a small commercial pad. They are still the best dated, public benchmarks available.
Montana DOT's Weighted Average Prices Catalog for calendar 2025 (dated January 2, 2026) includes these site work items:
| Item | Unit | Avg unit price | 2025 quantity |
|---|---|---|---|
| Clearing and grubbing | acre | $2,811.56 | 19.9 acres |
| Topsoil, salvaging and placing | CY | $6.25 | 153,146 CY |
| Excavation, unclassified | CY | $8.17 | 1,346,735 CY |
| Embankment in place | CY | $11.50 | 125,964 CY |
| Excavation, unclassified borrow | CY | $14.30 | 20,298 CY |
| Excavation, digouts | CY | $21.09 | 55,091 CY |
| Structure excavation, type 1 | CY | $75.00 | 540 CY |
| Crushed aggregate course | CY | $45.38 | 325,970 CY |
| Geotextile, stabilization | SY | $2.19 | 439,249 SY |
| RCP storm pipe, 18 in. | LF | $174.79 | 802 LF |
| RCP storm pipe, 24 in. | LF | $201.75 | 1,726 LF |
| Manhole structure base, 48 in. | each | $8,349.91 | 18 |
| Seeding, area no. 1 | acre | $769.04 | 293.2 acres |
| Erosion control blanket, short-term | SY | $3.50 | 10,957 SY |
| Dewatering | hour | $35.83 | 1,416 hours |
Oklahoma DOT's Weighted Average Item Price Report covering October 1, 2024 through March 31, 2026 (dated April 15, 2026) shows unclassified excavation at an average awarded price of $7.30 per cubic yard over about 10.9 million cubic yards, rock excavation at $11.66, unclassified borrow at $9.21, and trench excavation at $22.99.
Three lessons from these numbers:
- Quantity drives price. Mass excavation over a million yards prices in single digits per yard. Montana's structure excavation, on 540 yards, averaged $75.00. Small, confined digs cost several times more per yard.
- Trench work costs more than open cuts. Oklahoma's trench excavation item was about three times its unclassified excavation price.
- Pipe pay items are installed prices. A DOT pipe item is bid per foot in place, and the agency's specification defines what work is included with it. On private jobs, depth, trench support and bedding requirements drive the price as much as diameter.
For a deeper look at earthwork pricing, see our excavation cost per cubic yard analysis, which uses the same DOT data.
Cut and Fill Math
Comparing existing and proposed grades gives you bank volumes. The money is lost in what happens to those volumes once the dirt moves.
Shrink and swell
Soil swells when it is dug up and loaded, then compacts to less than its loose volume when placed and rolled. Depending on the material and the compaction spec, a yard of bank material may make less than a yard of compacted fill. The geotechnical report or lab testing should give you factors for your soils. If it doesn't, ask, because a site that balances at 1:1 on paper can be short of fill in the field.
A hypothetical example: a site needs 10,000 CY of compacted fill, and your cut is 10,000 bank CY. If the on-site clay compacts to 88% of its bank volume (an assumed factor for illustration), the cut yields only 8,800 CY of fill. The 1,200 CY shortfall has to be imported. Price that import at your local delivered and placed rate, and the gap can be a meaningful line item that a 1:1 assumption misses entirely.
Haul distance
The same yard of dirt costs more to move farther. Short dozer pushes are cheapest; scraper and articulated truck hauls cost more as distance grows; off-site haul adds trucking time and disposal or tipping fees. Look at the mass haul pattern before pricing: a site with cut in one corner and fill in the far corner is balanced in volume but not in cost.
Compaction and testing
Budget for third-party testing through the full earthwork duration, and price the risk of failed lifts. A failed density test means drying or moisture-conditioning, re-compacting and retesting, with machines and crews waiting. Wet seasons and silty or clay soils raise that risk.
Use the excavation calculator to check volumes and the grading and slope calculator to confirm pad and parking lot drainage before trusting your takeoff.
Sizing Contingency
A flat percentage applied to every site ignores what you actually know. Instead, list the specific risks on each site and size contingency to them:
- Geotech quality. A thorough report with adequate borings supports less contingency than a thin report or none.
- Rock indicated or suspected. Price it as a unit-price item or carry a specific allowance.
- Groundwater near excavation depth. Add dewatering time and compaction risk.
- Previously developed site. Expect buried debris, old utilities, and possible contaminated soil.
- Fill balance that depends on reusing on-site soils. If the soils turn out unsuitable, you buy import.
Write the basis down. When the owner asks why the site number is higher than another bidder's, you can point to specific risks instead of defending a percentage. For how contingency fits with markup and general conditions, see our construction cost estimating guide.
Unit Price vs. Lump Sum
Match the pricing method to how well the quantity is known.
Lump sum works for items measurable from the drawings: clearing limits, fine grading, erosion control, paving, and utilities shown on approved plans.
Unit prices protect both sides for items that can't be measured before digging: rock, undercut of unsuitable soils, imported fill, and dewatering. Bid them like a DOT item, with an estimated quantity, a unit price, and a stated method of measurement, so the owner pays for the quantity actually encountered. If an owner insists on a lump sum for these, price them at a conservative quantity and say so in writing.
Differing site conditions. On federal construction, FAR 52.236-2, Differing Site Conditions, gives the contractor a path to an equitable adjustment when subsurface or latent conditions differ materially from what the contract indicated (Type 1), or when unknown conditions of an unusual nature are encountered (Type 2). The clause requires written notice "promptly, and before the conditions are disturbed." On private work, there is no such clause unless you negotiate one, so ask for comparable language and follow its notice requirements exactly.
Final Checks Before You Submit
Before a site-heavy bid goes out:
- Recheck the largest quantities against the civil drawings and your own surface model.
- Compare your unit prices with recent job cost history and with public DOT data for scale.
- Confirm the shrink factor, import source and haul route.
- List every exclusion and every unit-price item in the bid letter.
- Run the full package through the cost estimator and compare the site share to similar past projects.
Frequently Asked Questions
How much does excavation cost per cubic yard?
On large highway quantities, Montana DOT's 2025 weighted average for unclassified excavation was $8.17 per cubic yard, and Oklahoma DOT's October 2024 to March 2026 average awarded price was $7.30. Small, confined, or residential digs cost more per yard because of mobilization, access and haul-off; Montana's structure excavation averaged $75.00 per yard on a small quantity.
How much does land clearing cost per acre?
Montana DOT's 2025 weighted average for clearing and grubbing paid by the acre was $2,811.56, on 19.9 acres. Actual cost depends heavily on tree size and density, disposal method (burning, grinding or hauling), and local rules.
How much contingency should I carry for site work?
Size it to the risks you can identify on each site: geotech coverage, rock, groundwater, prior development and reliance on on-site fill. Where possible, convert the biggest unknowns into unit-price items so the owner pays for what is actually found, which reduces the contingency you need to carry.
Is unit-price or lump-sum better for earthwork?
Use lump sum for quantities you can measure from the drawings and unit prices for subsurface unknowns such as rock, undercut, import and dewatering, with an estimated quantity and a defined method of measurement.
How do I estimate cut and fill volumes?
Compare existing and proposed surfaces on a grid or with takeoff software to get bank volumes, then apply shrink and swell factors from the geotechnical report or lab tests. A site that balances at 1:1 on paper is often short of compacted fill in the field.
What does storm pipe cost installed?
In Montana DOT's 2025 data, 18-inch reinforced concrete pipe averaged $174.79 per linear foot and 24-inch averaged $201.75, bid as in-place pay items on small quantities. Check what the agency's specification includes in the pipe item; on private jobs, depth, trench support and site access change the price.
