Concrete slab cost by size
The table below is the concrete slab calculator’s 2026 installed range including a compacted gravel base, vapor barrier, rebar reinforcement, forming, finishing, and control joints — a complete slab, not just the concrete. A 4-inch slab suits patios, sheds, and walkways; step up to 6-inch for a garage or anything carrying vehicle or heavy equipment loads.
| Slab size | Sq ft | 4-inch installed | 6-inch installed | Per sq ft (4″) |
|---|
| 10×10 | 100 | $2,250 – $3,550 | $2,450 – $3,850 | $23 – $36 |
| 12×12 | 144 | $2,500 – $4,200 | $2,800 – $4,450 | $17 – $29 |
| 16×20 | 320 | $4,000 – $6,650 | $4,300 – $7,000 | $12 – $21 |
| 20×20 | 400 | $4,650 – $7,750 | $5,100 – $8,250 | $12 – $19 |
| 24×24 | 576 | $6,050 – $9,950 | $6,850 – $11,050 | $10 – $17 |
| 30×40 | 1,200 | $11,400 – $18,550 | $13,050 – $20,850 | $9 – $15 |
Why small slabs cost more per square foot
Like most concrete work, the per-square-foot cost falls sharply as the slab gets bigger. A 10×10 pad runs $23–$36 per square foot, but a 30×40 shop floor drops to $9–$15. The reason is fixed cost: mobilizing a crew and a concrete truck, setting forms, and the minimum load charge cost about the same whether you pour 100 or 1,000 square feet, so a small pad has fewer feet to spread them over.
That is why the “$6 per square foot” figure you see quoted only holds on big pours. For a small pad, budget on the total, not the per-foot rate — and if you are pouring anyway, a slightly larger slab is cheap incremental square footage.
Frequently asked questions
How much does a concrete slab cost?
A complete concrete slab runs about $9–$36 per square foot installed in 2026 depending on size, including gravel base, vapor barrier, rebar, forming, finishing, and control joints. A small 10×10 pad runs $2,250–$3,550; a 20×20 slab $4,650–$7,750; a 30×40 shop floor $11,400–$18,550. Per-square-foot cost drops as the slab gets bigger.
How much does a 20x20 concrete slab cost?
A 20×20 (400 sq ft) slab runs about $4,650–$7,750 installed at 4 inches thick, or $5,100–$8,250 at 6 inches, in 2026. That includes a gravel base, vapor barrier, rebar, forming, finishing, and control joints — roughly $12–$19 per square foot.
How much does a concrete slab cost per square foot?
Installed cost runs about $9–$36 per square foot, but it is misleading on its own: a small 10×10 pad costs $23–$36 per foot because mobilization, forms, and the minimum load charge are near-fixed, while a 30×40 slab falls to $9–$15 per foot. Bigger pours are far cheaper per square foot.
How thick should a concrete slab be?
Four inches is standard for patios, sheds, and walkways; five to six inches for driveways and garages that carry vehicle loads; thicker for heavy equipment. A thicker slab adds concrete volume and cost — stepping a 20×20 from 4 to 6 inches adds roughly $450–$500 — but under-building a load-bearing slab invites cracking.
Does a concrete slab need rebar and a gravel base?
For any slab that carries load, yes. A compacted gravel sub-base spreads the load and drains water, a poly vapor barrier blocks ground moisture, and rebar or wire mesh controls cracking. These are standard line items in the ranges above; skipping them to save money is a common cause of premature cracking and settlement.
Planning your slab
- Patio, shed, or walkway? A 4-inch slab with a broom finish is standard.
- Garage or driveway? Step up to 5–6 inches with rebar for vehicle loads.
- Small pad? Budget on the total, not the per-foot rate — fixed costs dominate.
- Want it to look finished? Stamped, stained, or exposed-aggregate finishes cost more than broom.
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