Concrete Slab Foundation Cost Calculator
Get an instant free estimate for a concrete slab foundation (slab-on-grade) based on the footprint, slab type, reinforcement, and soil — for monolithic, stem-wall, and post-tensioned slabs.
Free Concrete Slab Foundation Cost Calculator
Use this calculator to calculate the cost of concrete slab foundation near you for free. Enter your ZIP code for a localized estimate.
Foundation Area
Enter the foundation footprint in square feet (the building's footprint). A small home/addition is ~800-1,200 sq ft; an average house is ~1,500-2,500 sq ft.
Slab Type:
Reinforcement / Thickness:
Site / Soil:
Additional Services:
Estimates are instant and require no contact information.
Based on inputs, your Concrete Slab Foundation project cost is approximately:
Note that the cost above is purely an estimate.
The actual cost may be higher or lower depending on the contractor's quote.
How Much Does Concrete Slab Foundation Cost?
A concrete slab foundation typically runs $6 to $14 per square foot installed, so an average 1,500 sq ft home slab lands around $9,000 to $21,000, with most standard projects clustering near $8 to $10 per foot. That price buys the full package: site prep and grading, a compacted gravel base, forms, reinforcement, the concrete pour, and finishing.
Two things move the number more than the size: the slab type and the soil. A monolithic slab on stable, flat ground sits at the bottom of the range; a post-tensioned or stem-wall slab on expansive or sloped soil — with engineered fill, deeper footings, and a soils report — pushes well past it. Add-ons like under-slab plumbing, slab insulation, a vapor barrier, and the permit stack on top. Use the calculator above to localize the estimate, then read on for what actually drives your quote.
Concrete Slab Foundation Cost by Size & Slab Type
Average Installed Cost by Footprint
| Foundation Size | Typical Cost | Notes |
|---|---|---|
| ~1,000 sq ft | $6,000 – $14,000 | Small home, addition, or garage. |
| ~1,500 sq ft | $9,000 – $21,000 | Average single-story house. |
| ~2,500 sq ft | $15,000 – $35,000 | Larger home footprint. |
| Poor / Expansive Soil | +30% & up | Post-tension, fill, engineering. |
Source: Baseline labor derived from U.S. Bureau of Labor Statistics, Cement Masons & Concrete Finishers (SOC 47-2051); ranges reflect our aggregated contractor quote data across U.S. markets.
Per-Square-Foot Rate by Slab Type
| Slab Type | Typical Rate | Best For |
|---|---|---|
| Monolithic | $6 – $9 / sq ft | Flat sites, warm climates, economy |
| Floating Slab | $7 – $10 / sq ft | Garages, sheds, additions |
| Stem-Wall | $8 – $12 / sq ft | Sloped lots, cold/frost climates |
| Post-Tensioned | $9 – $14+ / sq ft | Expansive clay & problem soils |
Source: U.S. Bureau of Labor Statistics, Cement Masons & Concrete Finishers (SOC 47-2051) for baseline labor, combined with our aggregated quote ranges from licensed foundation contractors. Regional adjustments applied via the calculator above.
The 6 Factors That Drive Your Quote
1. Footprint Size
A slab is priced per square foot of the building footprint, so square footage sets the baseline cost. But size scales predictably — doubling the area roughly doubles the concrete and labor. The slab type and soil are what swing the per-foot rate, which is why a small slab on bad soil can cost as much per foot as a large one on good ground.
2. Slab Type
Monolithic (slab and footing in one pour) is the economical default for flat, warm-climate sites. A stem-wall slab — footings and short walls first, then the slab — handles slopes and frost depth at a higher cost. A post-tensioned slab adds tensioned steel cables to resist soil movement and is the most expensive. The right type follows your climate, slope, and soil.
3. Soil & Site Conditions
Stable, well-draining soil on a flat lot needs only grading and a compacted base. Expansive clay, weak fill, rock, a high water table, or a sloped lot all add over-excavation, engineered fill, compaction, deeper footings, and often a geotechnical report and engineered design — frequently a 30%-plus premium and the single biggest cost wildcard.
4. Reinforcement & Thickness
A standard 4-inch slab with welded wire mesh is the baseline. Adding rebar improves strength and crack control; a thicker 6-inch-plus slab carries heavy loads (garages, equipment, brick veneer). More steel and more concrete cost more, but they're cheap insurance against the cracking that poor reinforcement invites on demanding sites.
5. Moisture & Utilities
A vapor barrier under the slab blocks ground moisture and is usually code-required under living space. Under-slab plumbing must be roughed in and sloped before the pour because it gets embedded. Slab-edge insulation matters in cold climates and under radiant heat. Each is a real, separately priced layer that's far cheaper to include now than to retrofit later.
6. Permits, Inspection & Engineering
A foundation is structural, so a permit and at least one pre-pour inspection (forms, steel, plumbing) are nearly universal. Expansive or problem soils often require a stamped engineer's design on top of the permit. These fees are modest next to the slab itself but are non-negotiable and should be in any honest quote.
Slab, Crawl Space, or Basement?
A slab isn't automatically the right foundation — it's the economical default where the climate and soil suit it. Here's the honest breakdown.
When a slab is the clear winner
- Warm or mild climates: with shallow frost depth, a monolithic slab is cheapest and quickest to build.
- Flat, stable lots: good soil needs little prep, keeping the per-foot rate at the bottom of the range.
- Budget-driven builds: a slab is the lowest-cost foundation and needs the least maintenance over time.
- Garages, additions & outbuildings: a floating or monolithic slab is usually all the structure needs.
When to consider an alternative
- Cold climates with deep frost: a stem-wall slab (or frost-protected design) may be required so footings sit below the frost line.
- Sloped or damp lots: a crawl space or stem-wall raises the structure and eases drainage and utility access.
- You want the space: a basement adds usable square footage that a slab simply can't — at a premium.
- Future utility access: crawl spaces and basements keep plumbing reachable; slab plumbing is embedded.
How to Vet and Hire a Foundation Contractor
A foundation is structural and unforgiving — mistakes are buried under your house. Before you hire:
- Verify state licensing and insurance. Confirm the contractor's license is active and that they carry general liability and workers' compensation coverage.
- Ask for a soils report — or who orders it. On anything but obviously good soil, a geotechnical test should drive the design, not guesswork.
- Confirm who designs and stamps it. Post-tensioned and problem-soil slabs require a licensed structural engineer's sealed design.
What a complete quote should spell out
- The slab type, thickness, and reinforcement (mesh vs. rebar vs. post-tension) in writing.
- Exactly what site prep is included: excavation, grading, fill, and compaction — and what happens if soil surprises appear.
- Whether the vapor barrier, under-slab plumbing rough-in, and insulation are in the price or extra.
- The concrete strength (psi), permit, inspections, and the curing/cure-time plan before framing begins.
Methodology & Sources
This calculator starts from a base per-square-foot rate set by your slab type (monolithic, floating, stem-wall, or post-tensioned), then applies a reinforcement/thickness multiplier and a soil/site multiplier before adding area-based and flat-fee add-ons(excavation, gravel base, insulation, vapor barrier, plumbing rough-in, and permits). The result is adjusted to your ZIP code's regional price level. In short: Footprint × (Slab Rate × Reinforcement × Soil) + Add-ons, localized by region. Baseline labor is anchored to federal wage data for concrete finishers and calibrated against our aggregated quotes from licensed contractors.
Data sources:
- U.S. Bureau of Labor Statistics — Cement Masons & Concrete Finishers (SOC 47-2051)
- American Concrete Institute (ACI) — Concrete Standards & Codes
- International Residential Code (IRC) — Chapter 4, Foundations
For a full explanation of how every calculator on this site is built and localized, see our methodology page.
About the Reviewer
Concrete & Paving Cost Estimator
Senior estimator for concrete flatwork, asphalt paving, and hardscape installations.
View full profile & credentials →Frequently Asked Questions
Installed, a slab-on-grade foundation runs roughly $6 to $14 per square foot once you include site prep, the gravel base, forms, reinforcement, concrete, and finishing. A simple monolithic slab on good, flat soil sits at the low end; a post-tensioned or stem-wall slab on poor or expansive soil sits at the top. For an average 1,500 sq ft home that's about $9,000 to $21,000. The slab type and the soil move the number far more than the size does.
A monolithic slab pours the floor and the thickened perimeter footing together in one shot — it's the fastest and cheapest, ideal for flat sites in warm climates. A stem-wall slab builds the footing and short foundation walls first, then pours the slab on top; it handles sloped lots and cold climates (footings below the frost line) but costs more. A post-tensioned slab embeds steel cables that are tensioned after curing to keep the concrete in compression — it's the go-to for expansive clay soils and the priciest of the three.
Because the slab rests directly on the ground, the soil has to provide stable, uniform support. Good, well-draining soil on a flat lot needs little more than grading and a compacted base. Expansive clay that swells and shrinks, weak or loose fill, or a sloped lot can crack or heave a slab — so they demand over-excavation, engineered fill, deeper footings, post-tensioning, and often a geotechnical (soils) report. That extra work can add 30% or more, which is why a soils test is worth doing before you pour.
If the slab sits under a bathroom, kitchen, or laundry, yes. The drain, waste, and water lines that come up through the floor have to be installed and sloped before the concrete is poured, because they get embedded. Get it right the first time — fixing a leak or moving a line later means saw-cutting and patching the slab. Budget for the plumbing rough-in as a separate line item; this calculator includes it as an add-on.
Almost always, and code usually requires it under living space. A 6-to-15-mil poly sheet goes over the gravel base before the pour to stop ground moisture from wicking up through the porous concrete. Skip it and you risk damp floors, condensation, mold, and failed flooring adhesives. It's a cheap layer — typically well under a dollar per square foot — that protects everything built on top.
A slab puts the house directly on concrete at grade — cheapest, quickest, low-maintenance, but no under-floor access (utilities are embedded) and best in warm climates. A crawl space raises the house a few feet, giving access to plumbing and wiring and suiting damp or sloped sites at a middle cost. A basement adds a full below-grade level — the most usable space and the best fit for cold climates, but the most expensive to dig and waterproof. Slab wins on economy; basement wins on space.
In cold climates, yes — and energy codes often require it. Rigid foam at the slab edge (and sometimes underneath) cuts the heat the ground pulls out of the slab, keeps floors warmer, and lowers heating bills. It's also important under any slab with radiant-floor heat. In warm climates it's less critical but can still help. It's offered here as an add-on so you can match it to your climate and code.
The pour itself is usually a single day, but the full job runs several days to a couple of weeks: site prep and grading, setting forms and the gravel base, the vapor barrier, plumbing rough-in, reinforcement, and an inspection all come first. After the pour, concrete is walkable in a day or two but keeps gaining strength for about 28 days; framing typically resumes after several days to a week of curing. Weather, soil prep, and inspection scheduling are the usual things that stretch the timeline.
Yes. A foundation is structural, so virtually every jurisdiction requires a building permit and at least one inspection — typically of the forms, reinforcement, and plumbing before the pour. The permit also ties the slab to the IRC/IBC requirements for footing depth, slab thickness, and reinforcement. Permit and inspection fees are included as an add-on here; on expansive or problem soil you may also need a stamped engineer's design.
Most slabs develop hairline shrinkage cracks that are cosmetic and normal. The cracks that matter are wide, offset, or actively moving ones tied to soil movement or settlement — those call for an evaluation by a structural engineer. Remedies range from epoxy or polyurethane injection to slab piers or helical piers that stabilize the soil beneath. Full replacement is rare and reserved for severe failure; pinpointing the soil cause first is what keeps a repair from recurring.