8-Inch Concrete Slab Cost 2026: $3,880 to $9,360 for a 20x20
An 8-inch concrete slab, 20x20 (400 sq ft), in 4,000 PSI concrete with a #4 rebar grid on a 6-inch stone base and broom-finished, costs about $5,690 installed. From the lowest published prices to the highest the range is $3,880 to $9,360 ($9.69 to $23.40 per sq ft). It takes 9.88 cubic yards, twice a 4-inch slab. The same slab at 6 inches is about $4,690.
8-Inch Slab Cost for Common Sizes
| Size | Concrete | Low | Typical | High | Per sq ft | Example use |
|---|---|---|---|---|---|---|
| 10x20 200 sq ft | 4.94 yd | $2,090 | $3,150 | $5,200 | $15.75 | Equipment pad |
| 20x20 400 sq ft | 9.88 yd | $3,880 | $5,690 | $9,360 | $14.23 | Two-car footprint, heavy use |
| 12x45 540 sq ft | 13.33 yd | $5,140 | $7,470 | $11,890 | $13.82 | RV pad, single coach |
| 14x50 700 sq ft | 17.28 yd | $6,560 | $9,460 | $14,740 | $13.51 | Long RV pad |
| 18x50 900 sq ft | 22.22 yd | $8,330 | $11,990 | $18,880 | $13.32 | RV pad plus side space |
| 30x50 1,500 sq ft | 37.04 yd | $13,650 | $19,480 | $30,700 | $12.99 | Large shop floor |
Every row: 8-inch slab, 4,000 PSI, #4 rebar at 18 inches each way, 6-inch crushed-stone base, broom finish, national prices. Low uses the lowest published price and our lowest labour assumption at every step; high uses the highest. The price per square foot falls with size because the fixed setup work is spread over more area. Engineering, a second rebar mat, excavation and permits are not included.
What Going from 4 or 6 Inches to 8 Inches Costs
| 20x20, rebar | Concrete | Typical | Low to high |
|---|---|---|---|
| 4-inch, 4-inch base | 4.94 yd | $3,910 | $2,590 to $6,350 |
| 6-inch, 4-inch base | 7.41 yd | $4,690 | $3,170 to $7,430 |
| 8-inch, 6-inch base | 9.88 yd | $5,690 | $3,880 to $9,360 |
Two inches more concrete adds 2.47 cubic yards on a 20x20, a heavier form and more placing time; our 8-inch spec also carries a deeper stone base. Together that is about $1,000 more than the 6-inch slab at typical prices. At $132.00 to $175.00 a yard for 4,000 PSI on the published lists, the concrete and truck charges alone are $1,369 to $2,739.
Crew time: our model allows 6 to 10 crew hours per 100 sq ft for an 8-inch slab (against 5 to 8.5 at 6 inches), plus 1.5 to 2.5 for the rebar grid. At $29.60 to $43.77 a crew hour (BLS wages plus employer costs) that is $1,125 to $2,889 of labour on a 20x20.
What the Code Says, and Who Decides
The model International Residential Code does not call for 8-inch slabs anywhere. R506.1 sets the minimum for a concrete floor on the ground at 3½ inches, lets slabs be designed to ACI 332 instead, and sends slabs on expansive soils to the foundation rules in R403.1.8. The code does not require reinforcement in a slab on the ground; where steel is used, R506.2.4 says it must be supported in the center to upper third of the slab while the concrete is placed.
So an 8-inch slab is a design decision for loads beyond ordinary cars: large motorhomes and trailers, heavy shop machines, vehicle lifts, or a slab the equipment maker specifies. Those loads arrive through small areas (tires, machine feet, lift posts), and the thickness, concrete strength and steel that carry them depend on the weights and on the soil underneath. For a heavy or unusual load, get the equipment maker’s slab requirements or have an engineer size the slab; a contractor’s rule of thumb is not a design.
The RV pad page covers pads by coach size, and the 6-inch slab page the standard vehicle spec.
More Concrete Means More Trucks
Because an 8-inch slab takes twice the concrete of a 4-inch one, it reaches multi-truck pours at half the area. At the 10 yards per truck our model assumes, a 20x20 needs 2 trucks, a 12x45 RV pad 2 and a 30x50 floor 4. Each truck must arrive while the edge of the last load is still workable, or the slab gets a cold joint, so ask how the contractor will schedule the trucks and where a joint will go if one is late.
Post-Tensioned Slabs Are Engineered, Not a Thickness Option
A post-tensioned slab uses high-strength steel tendons in sheaths, stressed after the concrete hardens. It is common on expansive clay, where a conventional slab can crack as the soil swells and shrinks. The 2025 California Residential Code requires post-tensioned slabs-on-ground to be designed to the Post-Tensioning Institute’s DC10.5 standard (R506.2), so it comes with an engineer’s design and a specialist crew. We have not priced it here; the post-tensioned slab cost page covers it.
How We Price a Slab
Every installed price on this site comes from one model: published ready-mix and materials prices, plus crew hours priced at Bureau of Labor Statistics wages, plus overhead and margin. The low figure uses the lowest published input and our lowest assumption at every step; the high figure uses the highest. The crew hours, overage and margin are our own estimates, not published figures, and are listed below so you can check them against your quote. Worked example: a 20 x 20 ft 8-inch slab (8-inch, 4,000 PSI, #4 rebar at 18 in, broom finish, 6-inch stone base).
| Line | Low | Typical | High | Basis |
|---|---|---|---|---|
| Ready-mix concrete | $1,369 | $1,582 | $1,901 | 9.88 cu yd plus 5 to 10% overage, at published per-yard prices |
| Delivery and small-load charges | $0 | $70 | $838 | Per-truck charges from the same price lists (10 yd per truck) |
| Crushed-stone base | $391 | $487 | $664 | 6 in compacted crusher run |
| Reinforcement | $297 | $297 | $297 | #4 bar at 18 in each way, laps and chairs |
| Form lumber | $48 | $72 | $95 | Perimeter boards, shared across reuses |
| Crew labour | $1,125 | $1,872 | $2,889 | Crew hours x BLS wages x employer costs |
| Overhead and margin | $646 | $1,314 | $2,674 | 20% to 40% on direct cost |
| Installed total | $3,880 | $5,690 | $9,360 | Rounded to the nearest $10 |
Not included: excavation and soil haul-off, removing an old slab, permits, pumping, decorative finishes and sealing. Totals are national; the calculators’ state option swaps in that state’s BLS wages and leaves concrete and materials at the published lists.
Published inputs (read 13 October 2026)
- Ready-mix, per cubic yard: 3,000 PSI $127.05 to $165.00, 4,000 PSI $132.00 to $175.00, from Supreme Concrete (Los Angeles, CA), Minimix Concrete (Pequannock, NJ), Gehring Construction & Ready-Mix (Columbus, NE, list dated 2026-01-01), Scenic City Ready Mix (Tennessee, list dated 2024-08-03).
- Small orders and trucks: short-load charge $50 under 4 yd (Gehring) or $100 at 5 yd or less, plus $100 more at 2 yd or less (Scenic City); per truck, no charge within 20 miles (Gehring), a $35 surcharge (Scenic City), or $363.88 Zone A delivery plus a $55 environmental fee (Supreme).
- Crushed-stone base: $44.00 to $74.75 per cubic yard from D & L Supply (Central New York, $44.00/yd), JMJ Companies (Lynchburg, VA, $39.50/ton), Golden Landscaping Supply (Cumming, GA, $50.00/ton), Yard Works Landscape Supply (Fort Mill, SC, $74.75/yd); per-ton prices converted at 2,450 lb per yard.
- Steel, forms, poly: #4 rebar 20 ft $8.99, 6x6 10-gauge mesh 4x8 panel $6.99, 2x6x12 $14.32, 2x4x16 $12.13, 6-mil poly 8 ft 4 in x 100 ft $59.99, rebar chair $0.33 (Menards online prices; Home Depot and Lowe’s pages could not be read that day). That works out to $0.24 per sq ft for mesh and $0.74 per sq ft for a rebar grid, materials only.
- Wages: BLS OEWS 47-2051 cement masons (May 2025) 25th percentile $22.60, median $27.41, 75th $32.15 an hour; 47-2061 construction laborers $18.57, $22.66, $28.72. Employer costs from BLS ECEC June 2026, construction industry ($51.96 total compensation per $36.13 of wages, x1.44): a crew hour costs $29.60 to $43.77.
Our assumptions (estimates, not published figures)
- Crew: half cement masons, half laborers.
- Setup per job: 8 to 16 crew hours (layout, stripping, cleanup).
- Per 100 sq ft: 4-inch 4 to 7 crew hours, 6-inch 5 to 8.5, 8-inch 6 to 10; add 0.5 to 1 for mesh or 1.5 to 2.5 for rebar.
- Concrete overage 5% to 10%; base stone ordered at 1.2x its compacted volume; form boards charged at half to all of their price.
- Overhead and margin 20% to 40% of direct cost.
- 6-inch and thicker slabs use 4,000 PSI mix; thinner slabs 3,000 PSI.
Sources: BLS OEWS 47-2051 cement masons (May 2025), BLS OEWS 47-2061 construction laborers (May 2025), BLS ECEC, construction (June 2026), ready-mix price lists from Supreme Concrete, Minimix Concrete, Gehring Construction & Ready-Mix, Scenic City Ready Mix, crusher-run prices from D & L Supply, JMJ Companies, Golden Landscaping Supply, Yard Works Landscape Supply, Menards rebar and lumber prices, IRC R506.1 and R506.2.4 (2018 IRC as adopted in the Minnesota Residential Code 2020, published by UpCodes), 2025 California Residential Code R506.2. All read 13 October 2026. Crew hours, overage, truck size, overhead and margin are our estimates and are listed in the method above.