Concrete Foundation Cost Calculator
Rough budget estimate for a slab-on-grade foundation pour — material and labor only. Always verify thickness and reinforcement with a structural engineer.
How this calculator works
This gives a rough material-and-labor budget for a flat slab-on-grade foundation pour: cubic yards of concrete (from the standard slab-volume formula) times your price per cubic yard, plus labor (building footprint area times a per-square-foot rate). It does not model footings, reinforcement, or engineering requirements.
Formula: Cubic yards = (Length ft × Width ft × Depth ft) ÷ 27. Total cost = (Cubic yards × Price/yd³) + (Area sq ft × Labor rate/sq ft).
Worked example
A 40 ft × 20 ft (800 sq ft) slab at 6 inches, $160/yd³ material, $8/sq ft labor:
- Depth in feet: 6 ÷ 12 = 0.5 ft
- Cubic yards: (40 × 20 × 0.5) ÷ 27 ≈ 14.8148 → 14.81 yd³
- Material cost: 14.8148 × $160 ≈ $2,370.37
- Labor cost: 800 × $8 = $6,400.00
- Total estimated cost: $8,770.37
Cost reference (at default rates)
| Foundation size | Estimated total cost |
|---|---|
| 20 ft × 10 ft | ~$2,193 |
| 40 ft × 20 ft | ~$8,770 |
| 80 ft × 40 ft | ~$35,081 |
How to measure your area
Use the full building footprint in feet, matching the dimensions on your foundation plan rather than a rough pace-off. Because real foundation costs depend heavily on footing depth, soil type, and reinforcement that this calculator doesn’t model, treat this number strictly as a starting-point budget check before getting a contractor’s bid.
Frequently asked questions
Is this estimate a substitute for an engineer's foundation design?
No. This is a rough slab-on-grade material-and-labor budget only. Actual foundation thickness, reinforcement, footing depth, and vapor barrier requirements depend on soil conditions, local frost depth, and building code, and must be specified by a structural engineer or stamped foundation plan — never rely on this calculator to size a real foundation.
What does this estimate exclude?
Thickened perimeter footings, rebar or post-tension cable, a vapor barrier, gravel sub-base, excavation, and permit/inspection fees are all excluded. A real foundation bid will price each of these as separate line items, often adding significantly to the flat-slab number shown here.
Why is the price per cubic yard higher than the patio or driveway default?
Foundation-grade concrete often uses a higher-strength mix and is typically pumped or placed with more care than flatwork, so this defaults to $160/yd³ versus $150/yd³ for patios and driveways. Adjust to your ready-mix supplier's actual foundation-mix quote.
What thickness is typical for a slab-on-grade foundation?
6 inches is a common default for a monolithic slab-on-grade under a house, thicker than the 4-inch standard for patios and driveways. Thickened edges under load-bearing walls are usually 12+ inches deep and are not captured by this flat-depth estimate.
How is this different from the Concrete Footing Calculator?
The Concrete Footing Calculator sizes a linear footing (a trench of a given width and depth around a perimeter). This calculator estimates a flat slab across the whole building footprint — for a footed foundation, you likely need both calculators and should add their totals.
Estimates only. Verify quantities with your supplier before purchasing.