Concrete Foundation Cost Calculator
A concrete foundation cost calculator adds cubic yards × price per yd³ to area × labor rate: 40 × 20 ft at 6 in is 14.81 yd³, or $8,770 at default rates.
Concrete foundation cost calculator: concrete + labor
This concrete foundation cost calculator gives a first budget for a flat slab-on-grade foundation. The formula is total = (cubic yards × price per yd³) + (square feet × labor rate). Cubic yards come from length × width × (depth ÷ 12) ÷ 27. The quantity line shows cubic yards; the cost line shows concrete and labor added together. It does not add waste, so order slightly more concrete than the result.
The two halves of the estimate
Concrete. The calculator finds the slab’s volume. A 6 in slab is 0.5 ft thick, so every 54 sq ft of footprint takes 1 cubic yard. It multiplies that volume by your price per yard, which defaults to $160.
Labor. It multiplies the footprint area by a flat labor rate, which defaults to $8 per sq ft. Think of that rate as covering forming, placing, finishing, and curing. If your contractor quotes rebar, vapor barrier, or base prep inside the labor price, use their all-in rate here.
Worked examples
- Default: 40 × 20 ft slab, 6 in thick, $160/yd³, $8/sq ft labor
- Area: 40 × 20 = 800 sq ft
- Volume: 800 × 0.5 = 400 cu ft ÷ 27 = 14.81 yd³
- Concrete: 14.815 × $160 = $2,370.37
- Labor: 800 × $8 = $6,400.00
- Total: $8,770.37
- Detached garage: 30 × 24 ft slab, 6 in thick, same rates
- Area: 30 × 24 = 720 sq ft
- Volume: 720 × 0.5 = 360 cu ft ÷ 27 = 13.33 yd³
- Concrete: 13.333 × $160 = $2,133.33
- Labor: 720 × $8 = $5,760.00
- Total: $7,893.33
Ready-mix is ordered in quarter or half yards, so a 13.33 yd³ slab would usually be ordered at 14 yd³ or more to cover an uneven base.
Foundation size reference at default rates
| Slab (6 in thick) | Area | Concrete | Concrete cost | Labor | Total |
|---|---|---|---|---|---|
| 20 × 10 ft | 200 sq ft | 3.70 yd³ | $593 | $1,600 | $2,193 |
| 30 × 24 ft | 720 sq ft | 13.33 yd³ | $2,133 | $5,760 | $7,893 |
| 40 × 20 ft | 800 sq ft | 14.81 yd³ | $2,370 | $6,400 | $8,770 |
| 50 × 30 ft | 1,500 sq ft | 27.78 yd³ | $4,444 | $12,000 | $16,444 |
Rates are the calculator’s defaults, not market prices. Replace both with local quotes.
What to add outside the calculator
| Item | Why it changes the cost |
|---|---|
| Thickened edges and interior footings | Extra concrete below the slab line |
| Rebar or wire mesh | Material plus labor to place and tie |
| Vapor barrier | Sheet goods under the slab |
| Gravel base | Several inches of compacted stone |
| Excavation and grading | Machine time and haul-off |
| Pump truck | Needed when trucks cannot reach the forms |
| Permits and inspections | Set by your local building department |
How to measure a foundation
- Use plan dimensions. Take the outside-of-slab size from the foundation plan, not a pace-off.
- Split L-shapes. Price each rectangle separately and add the totals.
- Measure thickness of the slab field. Price thickened edges separately with the concrete footing calculator.
Turning the estimate into a real budget
Use this calculator for the slab itself, then build up the rest line by line. Add the perimeter footing concrete from the footing calculator, priced at the same rate per yard. Ask your supplier for a delivered price per yard that includes fuel and any short-load or weekend charges.
Next, get a labor quote that states what it covers. Some contractors include forming, steel, vapor barrier, and finishing in one price per square foot. Others itemize them. Put that all-in rate into the labor box so the total reflects the actual scope. Finally, add a contingency for soil surprises, which you will not know about until digging starts.
Common estimating mistakes
- Pricing a flat slab as a whole foundation. Footings can add a large share of the concrete.
- No overage. Subgrade is never perfectly flat. Many contractors order 5 to 10% extra concrete.
- Ignoring delivery minimums. Small loads often carry a short-load fee.
- Comparing bids with different scopes. Ask every contractor to list base, steel, barrier, and finish separately.
For deeper foundations, compare with the basement foundation cost calculator or the pier and beam foundation cost calculator.
This is a budgeting tool. Foundation design depends on soil, loads, and local code; have it specified by a licensed structural engineer.
Frequently asked questions
Is this estimate a substitute for an engineer's foundation design?
No. It is a rough slab material-and-labor budget. Real foundation thickness, footing size and depth, reinforcement, and vapor barrier depend on soil, frost depth, loads, and local code. Those must come from a structural engineer or approved foundation plan.
What does this estimate exclude?
Thickened edges and perimeter footings, rebar or post-tension cables, vapor barrier, gravel base, excavation, forming lumber, pump truck fees, and permits are all outside the formula. Add them as separate lines, or raise the labor rate to cover them.
Why is the default price per cubic yard $160?
It is a placeholder slightly above the $150 default used for patios and sidewalks, since foundations often specify a stronger mix. Ready-mix prices vary widely by region and order size, so replace it with your supplier's quote, including any short-load or delivery charges.
What thickness is typical for a slab-on-grade foundation?
Many house slabs are 4 to 6 inches thick in the field, with thickened edges or footings under load-bearing walls that are much deeper. The required thickness depends on your local code and engineering, so check local code before choosing a depth.
How is this different from the concrete footing calculator?
The footing calculator sizes a strip of concrete around the perimeter. This calculator prices a flat slab over the whole footprint. A monolithic slab with thickened edges needs both: price the slab here and add the footing volume from the footing calculator.
Why does labor cost more than concrete in the estimate?
Because the default labor rate of $8 per sq ft is applied to every square foot, while concrete is priced by volume. For the default 800 sq ft slab, labor is 800 × $8 = $6,400 and concrete is 14.81 yd³ × $160 = $2,370. Change either rate to match your bids.
Estimates only. Verify quantities with your supplier before purchasing.