An excavation takeoff turns the plans into quantities you can price: topsoil to strip, the main dig, footing excavation, backfill around the foundation, and what's left to haul off. The basic method is area × depth for each item, with the dig enlarged for working room and side slopes, everything kept in bank cubic yards, and then shrink and swell applied for backfill and trucking.
Below is a full residential example with every number shown, a summary table, and the mistakes that most often throw an excavation number off.
The example house
Example: a house with a full basement on a fairly flat lot. All dimensions are invented for the example, but the math is real.
| Item | Value |
|---|---|
| Basement footprint (outside of foundation wall) | 28 ft × 40 ft |
| Foundation wall | 8 in thick |
| Perimeter footing | 24 in wide × 10 in thick, centered on the wall |
| Interior column pads | 3 pads, 3 ft × 3 ft × 12 in deep |
| Existing grade over the dig | averages elevation 100.0 |
| Topsoil | 6 in, stripped and stockpiled on site |
| Subgrade (bottom of under-slab gravel, top of footing) | 8.0 ft below stripped grade |
| Working room (overdig) | 3 ft past the outside face of the wall |
| Side slopes | 1:1 (1 ft horizontal per 1 ft vertical) |
| Shrink for compacted backfill | 10% (placeholder) |
| Swell for hauling | 25% (placeholder) |
| Truck capacity | 12 loose CY |
The side slope is a safety decision as much as an estimating one. OSHA's excavation standard (29 CFR 1926 Subpart P, Appendix B) sets maximum allowable slopes by soil type for excavations under 20 ft deep: 3/4:1 for Type A soil, 1:1 for Type B, and 1½:1 for Type C. Your competent person and the geotech decide the real slope. We use 1:1 here.
The shrink and swell factors are placeholders. Use the geotech report or your own history for your soil.
Step 1: Topsoil strip
Strip the building area plus room for the dig, the stockpile and equipment. Here that's an 80 × 100 ft area.
- 80 × 100 = 8,000 SF
- 8,000 × 0.5 ft = 4,000 CF ÷ 27 = 148.1 CY (bank)
This topsoil gets stockpiled and respread later, so it's not haul-off. Keep it out of the excavation total. In the pile it takes up more room: at a 25% swell it's roughly 185 loose CY, which matters when you're deciding where on a tight lot the pile goes.
Step 2: Basement mass excavation
Bottom of the hole
The hole bottom is the foundation footprint plus working room on all sides:
- 28 + 3 + 3 = 34 ft
- 40 + 3 + 3 = 46 ft
- Bottom area = 34 × 46 = 1,564 SF
Top of the hole
With 1:1 slopes and 8.0 ft of depth, the top grows 8 ft on every side:
- 34 + 16 = 50 ft
- 46 + 16 = 62 ft
- Top area = 50 × 62 = 3,100 SF
Volume
A sloped-sided rectangular hole is a frustum. The prismoidal formula is the accurate way:
V = depth ÷ 6 × (A_bottom + 4 × A_mid + A_top)
The mid-depth outline is 42 × 54 ft (4 ft of slope on each side), so A_mid = 2,268 SF.
- V = 8 ÷ 6 × (1,564 + 4 × 2,268 + 3,100)
- V = 1.333 × (1,564 + 9,072 + 3,100) = 1.333 × 13,736 = 18,315 CF
- 18,315 ÷ 27 = 678.3 CY (bank)
If you used average end area instead, (1,564 + 3,100) ÷ 2 × 8 = 18,656 CF = 691.0 CY, about 13 CY high. Not a big deal on one house, but it's a consistent bias.
What if the lot isn't flat?
Take the existing elevation at the four corners of the dig (and the center on a lumpy lot), average them, subtract the stripping depth and the subgrade elevation, and use that as the depth. On a lot that falls more than a couple of feet across the dig, split the hole into sections or use a grid method.
Step 3: Footing excavation
In this example the hole is dug to subgrade (bottom of the under-slab gravel, which here is also top of footing), and the footings are trenched below that.
Perimeter footing
The footing is centered on the wall, so measure its length along the wall centerline. The centerline is 4 in (0.333 ft) inside the outside face on every side:
- 28 − 0.667 = 27.333 ft
- 40 − 0.667 = 39.333 ft
- Centerline perimeter = 2 × (27.333 + 39.333) = 133.3 LF
- Trench: 133.3 × 2.0 ft wide × 0.833 ft deep = 222.2 CF ÷ 27 = 8.2 CY
Column pads
- 3 × (3 × 3 × 1.0) = 27 CF ÷ 27 = 1.0 CY
Many crews just dig the whole hole to bottom of footing instead of trenching. If yours does, add the extra depth to the mass dig and carry more under-slab stone. Don't count both.
Step 4: Foundation backfill
Backfill goes in the space between the foundation wall and the sloped sides of the hole, from subgrade up to stripped grade. Take the hole volume and subtract what the basement occupies:
- Hole: 18,315 CF
- Basement block from subgrade to stripped grade: 28 × 40 × 8.0 = 8,960 CF
- Backfill space = 18,315 − 8,960 = 9,355 CF ÷ 27 = 346.5 CY (compacted, in place)
The footings sit below subgrade, in their own trenches, so they don't take up backfill space here.
Backfill is placed and compacted, and compacted soil takes less room than the same soil in the bank. At 10% shrink:
- Bank yards needed = 346.5 ÷ 0.90 = 385.0 BCY
Step 5: Haul-off
- Total excavated (bank): 678.3 + 8.2 + 1.0 = 687.5 BCY
- Reused as backfill (bank): 385.0 BCY
- Haul-off (bank): 687.5 − 385.0 = 302.5 BCY
- Haul-off (loose) at 25% swell: 302.5 × 1.25 = 378.1 LCY
- Truck loads at 12 LCY: 378.1 ÷ 12 = 31.5, so 32 loads
If the spoil can't be used as backfill
If the geotech or spec calls for granular backfill against the wall, or the native soil is expansive clay, the whole dig leaves the site:
- 687.5 BCY × 1.25 = 859.4 LCY ÷ 12 = 71.6, so 72 loads out
- Plus 346.5 CY of compacted backfill material brought in (order it in the supplier's units, with your compaction factor)
That one note in the geotech more than doubles the trucking. Read it before you price.
Summary table
| Item | Quantity | Unit | Notes |
|---|---|---|---|
| Topsoil strip | 148.1 | BCY | 8,000 SF × 6 in; stockpile and respread |
| Basement mass excavation | 678.3 | BCY | 34 × 46 bottom, 1:1 slopes, 8 ft deep, prismoidal |
| Footing excavation | 8.2 | BCY | 133.3 LF × 2 ft × 10 in |
| Column pad excavation | 1.0 | BCY | 3 pads |
| Total excavation | 687.5 | BCY | |
| Foundation backfill | 346.5 | CCY | 385.0 BCY of spoil at 10% shrink |
| Haul-off | 302.5 | BCY | 378.1 LCY, 32 loads at 12 LCY |
| Topsoil respread | 148.1 | BCY | Same pile, final grading |
Label every number BCY, LCY or CCY. "Yards" with no unit is how a 25% error gets into a bid.
Common excavation takeoff mistakes
- Digging to the footprint. The house is 28 × 40, but the hole isn't. Without overdig and slopes, this hole would be 28 × 40 × 8 = 8,960 CF (332 CY), less than half the real 678 CY. Even with overdig but vertical sides (34 × 46 × 8 = 463 CY), you'd be 215 CY short.
- Mixing bank and loose yards. Pricing haul-off on bank yards undercounts trucks by the swell factor.
- Forgetting shrink on backfill. 346.5 CY of compacted backfill needs 385 bank yards, not 346.5.
- Counting topsoil as haul-off. If it's being respread, it stays on site. If the lot is tight and it has to leave and come back, that's two haul lines.
- Double-counting footings. If the hole is dug to bottom of footing, there is no separate footing trench.
- Wrong depth reference. Depth runs from stripped grade (not existing grade) to subgrade (not top of slab).
- Skipping the geotech. Groundwater, rock, unsuitable soil and over-excavation requirements change the number more than any formula does.
- Average end area on a deep hole. It runs high on sloped-sided pits. Use the prismoidal formula.
Doing it from the plans
The inputs for every line above come from the plan set: footprint and wall thickness from the foundation plan, footing sizes from the structural details, finished floor and grades from the grading plan, topsoil depth and soil notes from the geotech.
In Foreman AI you upload the whole set and ask for those numbers in plain English ("What are the footing dimensions and what does the geotech say about backfill?"), with answers citing the sheet. In Takeoff Studio, the cubic-yard dig tool does flat-bottom digs (basements, pits, ponds) by area × depth and carries a swell factor so you get bank and truck yards together. For a sloped hole like this one, run the prismoidal formula, or trace the outline at mid-depth as a close approximation (42 × 54 × 8 here gives 672 CY, about 1% under). Area tools handle the topsoil strip and linear tools handle trenches and silt fence. If the lot needs real grading too, the earthwork takeoff works cut and fill from the grading plan's contours. The background on that is in how to read a grading plan.
Upload a plan set and try it free. No card required.
FAQ
How do you calculate excavation for a basement?
Start with the foundation footprint, add working room on every side (often 2 to 3 ft past the wall), then add side slopes based on soil type and depth. Use the prismoidal formula for the sloped hole, and keep the result in bank cubic yards before applying swell for hauling.
How much overdig do you need for a basement?
It depends on the crew and the forming system, but 2 to 3 ft past the outside of the foundation wall is a common allowance for forming, waterproofing and drain tile. Side slopes for safety are added on top of that.
How do you calculate haul-off for excavation?
Subtract the bank yards you'll reuse as backfill (compacted backfill volume divided by one minus the shrink factor) from the total bank yards excavated. Multiply what's left by one plus the swell factor for loose yards, then divide by truck capacity.
What is the difference between bank, loose and compacted yards?
Bank yards are soil in the ground before digging. Loose yards are the same soil after it's dug, which takes more room, so trucks haul loose yards. Compacted yards are soil placed and compacted, which usually takes less room than bank. One pile of dirt has three different volumes depending on where it is.