Cost to Pour a Concrete Slab: Per Square Foot & by Size
By Marko VisicBSc Physics, University of Ljubljana
Slab quotes swing with region, finish and access, but the installed cost has a traceable baseline: the national materials model plus the Census cost structure. Here is what a slab costs, and how little of that is the concrete itself.
A plain 4-inch slab on a 4-inch base runs about $6.42/sq ft installed, so a 12-foot-square slab lands near $920. The ready-mix concrete is only about $1.64 per square foot of that. Most of a slab’s price is everything but the concrete: forming, labor, finishing and overhead.
$6.42/ft²
per square foot installed: a plain 4-inch slab on a 4-inch base
Concrete cost per square foot for a slab
As of Oct 2026, a plain slab-on-ground works out to about $6.42/sq ft installed for a 4-inch slab on a 4-inch base, from the national materials model divided by the Census materials share. That is a national baseline, not a local quote. Access, finish and region move a real bid.
Cost by slab size
Installed cost scales with area. These are plain slabs on a 4-inch base at the national model value, at 4-, 5- and 6-inch thicknesses: a baseline to size a budget, before finish or removal.
| Slab size | Area (sq ft) | Installed, 4 in | Installed, 5 in | Installed, 6 in |
|---|---|---|---|---|
| 10 × 10 ft | 100 | $640 | $770 | $900 |
| 12 × 12 ft | 144 | $920 | $1,110 | $1,300 |
| 16 × 16 ft | 256 | $1,640 | $1,980 | $2,310 |
| 20 × 20 ft | 400 | $2,570 | $3,090 | $3,610 |
| 20 × 30 ft | 600 | $3,850 | $4,640 | $5,420 |
| 24 × 24 ft | 576 | $3,700 | $4,450 | $5,200 |
| 30 × 30 ft | 900 | $5,780 | $6,960 | $8,130 |
| 30 × 40 ft | 1,200 | $7,700 | $9,270 | $10,840 |
| 40 × 60 ft | 2,400 | $15,410 | $18,550 | $21,690 |
Cost of a 4-inch-thick 30 by 30 concrete slab
A 900 square feet slab at four inches lands near $5,780 installed at the national model, plain finish on a 4-inch base, before delivery, finishing or removal. It is one of the most-asked sizes because it suits a detached garage or a shop floor; a local bid moves with access, finish and region, so treat this as the baseline to judge quotes against.
What is in the price
The installed price follows the US Census cost structure for the concrete-contractor industry (NAICS 238110). Materials (the concrete, base and steel together) are only 34.5% of the work; payroll and benefits are 28.4%, with subcontracts, fuel, overhead and margin making up the balance.
| Cost component | Share of price |
|---|---|
| Materials (concrete, base, steel) | 34.5% |
| Payroll & benefits | 28.4% |
| Subcontracts | 9.7% |
| Fuel | 2.8% |
| Other operating, depreciation & rentals | 8.6% |
| Residual (overhead & margin) | 15.9% |
Thickness and cost
Code sets a minimum slab-on-ground thickness of 3½ inches over a 4-inch gravel base. Thickness drives the concrete share directly: at the national value the concrete runs about $1.64 per square foot for a 4-inch slab and $2.46 per square foot for a 6-inch slab. Going from four to six inches adds about $0.82 per square foot of concrete. See the slab thickness guide for when to pour thicker.
Concrete slab foundation cost
A slab-on-grade can itself be the foundation, a monolithic or floating slab that carries a garage or small building directly on grade, and the per-square-foot figures above are exactly that. They do not cover a frost-wall, stem-wall or full basement foundation: that is a different structure (footings below the frost line, poured or block walls, and the excavation and backfill around them), priced by its own linear foot of wall and its depth, not by slab area. No single national figure covers those here, so treat this page as the slab-on-grade baseline and price a deep foundation separately with a local contractor.
Cost to install a concrete pad
A concrete pad (for a shed, an air-conditioner condenser, a generator or a hot tub) is just a small slab-on-grade, so the same per-square-foot baseline applies. What changes at small sizes is the mix choice: a short ready-mix load can pick up a small-load (short-load) fee, so for a pad of only a few bags’ worth, bagged concrete often comes out cheaper than a delivered yard. The bags-per-yard guide and the concrete-bags calculator work that breakeven; for a hot-tub pad, the hot-tub pad guide covers thickness and reinforcement.
Finishes and extras
Finishes and add-ons sit on top of the plain-slab baseline. Public-agency price lists give sourced examples: Montana paid $112.00 per square yard for colored sidewalk concrete and Vermont $268.16 per square yard for a stamped island. Reinforcement (where provided, it must be supported in position before the pour) and a 10-mil vapor retarder under an enclosed floor add material and labor; driveways, walks and patios need no vapor retarder.
Removing an old slab first
If you are replacing a slab, demolition and haul-off come first. Louisiana DOT contracts put removal of concrete walks and drives at $22.76 per square yard, a public-contract rate that, like the finishes above, carries prevailing wages and runs above small residential jobs. It is a separate line from the new pour.
Bags vs ready-mix for small slabs
For a small slab, bagged mix can beat a short ready-mix load, because small orders pick up a flat small-load fee per delivery. Whether it does turns on your bag price. The bags-per-yard guide and the concrete-bags calculator work the breakeven.
Cost by project
Slab cost drives several specific jobs. For a full installed estimate with size, thickness and state, use the concrete slab cost calculator. For project-specific numbers, see the patio cost guide, the driveway cost guide, and the hot-tub pad guide.
Concrete slab cost FAQ
How much does it cost to pour a concrete slab?
About $6.42/sq ft installed for a plain 4-inch slab on a 4-inch base, so a 12-foot-square slab runs near $920. Finishes, removal and a thicker pour add to that.
How much is concrete per square foot?
The concrete alone is about $1.64 per square foot for a 4-inch slab. Installed, a slab is about $6.42/sq ft. Most of the price is forming, labor and finishing.
How thick should a concrete slab be?
Code sets a floor of 3½ inches for a slab-on-ground, over a 4-inch gravel base; go thicker for heavy loads. See the slab thickness guide.
What is the biggest part of a slab’s cost?
Not the concrete. In the Census cost structure, materials are only 34.5% of the installed price: labor, forming, finishing and overhead make up the rest.
Sources & method
- U.S. Census Bureau. 2022 Economic Census, table EC2223BASIC 'Construction: Summary Statistics for the U.S., States, and Selected Geographies: 2022' (variables RCPCWRK 'Value of construction work ($1,000)', CSTMPRT, PAYANN, BENEFIT). Reference year 2022
- U.S. Census Bureau. 2022 Economic Census, Selected Sectors: Industry by Products for the U.S. and States (table EC2200NAPCSINDPRD), NAICS 327320 × NAPCS 2040575000, United States, all establishments. 2022 (Economic Census; product tables released May 2025)
- U.S. Bureau of Labor Statistics, via FRED (Federal Reserve Bank of St. Louis). FRED series PCU327320327320, text data file. Sep 2026 value (updated Oct 15, 2026)
- U.S. Geological Survey. Mineral Commodity Summaries 2026 — Stone (Crushed), Salient Statistics—United States (columns 2021, 2022, 2023, 2024, 2025e). 2025 estimate; MCS 2026 ver. 1.0 published Feb 6, 2026 (ver. 1.1 March 2026)
- U.S. Bureau of Labor Statistics, via FRED. FRED series WPU1321, Producer Price Index by Commodity: Nonmetallic Mineral Products: Construction Sand, Gravel and Crushed Stone. Sep 2026 value (updated Oct 15, 2026)
- Storey County (NV) Community Development. Slab / Slab-Gravel Inspection Checklist (cites IRC R506.1). Checklist dated May 5, 2022 (IRC edition adopted by Storey County)
- Culpeper County (VA) Building Department. Letter 'Vapor Retarder': approved modification of 2021 Virginia Residential Code §R506.2.3 (R. Grace, CBO). Feb 20, 2026
- State of South Carolina (Building Codes Council regulation), via Cornell LII. S.C. Code Regs. § 8-1225 – IRC R506.2.3 Vapor Retarder (exceptions). State Register Vol. 46, Issue 05, eff. May 27, 2022
- City of American Canyon (CA). Municipal Code §16.03.070 'Amend Section R506.2.4 Reinforcement support' (Ord. May 2022; California Residential Code). 2022 (Ord. May 2022)
- Vermont Agency of Transportation. 5 Year Averaged Price List, October 2021 - October 2026. Oct 2021-Oct 2026
- Montana Department of Transportation. Weighted Average Prices Catalog, CY2025. CY2025
- Louisiana Department of Transportation and Development. Weighted Averages, Weighted Unit Price for 3rd Quarter 2026. 10/1/2025-9/30/2026
- National Ready Mixed Concrete Association. CIP 8 – Discrepancies in Yield. 2016 (1979, 1991, 2000, 2016)
Installed cost is the national materials model (concrete at the producer value plus a base course) divided by the 34.5% Census materials share; concrete-only cost is the ready-mix value times the thickness, divided by 324. Finish, removal and code figures are from state-DOT price lists and the IRC. Full method is on the methodology page.
- Concrete Slab Cost CalculatorInstalled cost for your exact slab, size, thickness and state.
- Concrete Slabs GuideThickness, PSI, reinforcement, base and joints in one place.
- How Thick Should a Slab Be?Code minimums and when to pour thicker.
Marko Visic
I'm Marko Visic, a physics graduate who builds data-driven calculators. I run ConstructionCalc through my company, Moving Data Systems d.o.o.
The calculators help you plan a DIY job or check a contractor's quote before you sign. Each one cites its sources and shows its method, and cost figures are computed from public primary data. If a number looks wrong, email info@constructioncalc.org and I'll trace it to its source or fix it.