How Much Does a 30x40 Concrete Slab Cost?
A 30x40 concrete slab costs about 7,200 to 14,400 dollars installed in 2026, or roughly 6 to 12 dollars per square foot across its 1,200 square foot footprint. A basic 4 inch broom finish sits at the low end, while a 6 inch reinforced pour with site prep runs higher. Below is the cost broken down by thickness, labor versus materials, the add-ons that move the number, and a calculator that sizes your exact pour.
Key takeaways
- A 30x40 slab is 1,200 square feet and costs about 7,200 to 14,400 dollars installed in 2026, most projects landing near 8 to 10 dollars per square foot.
- A 4 inch slab needs about 14.8 cubic yards of concrete; a 6 inch slab needs about 22.2 cubic yards, roughly 50 percent more material.
- Labor is 40 to 50 percent of the total; thickness mainly raises the material share, not the labor.
- Rebar or wire mesh adds about 240 to 600 dollars; a gravel base adds 1,200 to 2,400 dollars.
- Coastal and Northeast markets run 20 to 40 percent above the Midwest and South for the same slab.
The total cost of a 30x40 concrete slab in 2026
A 30 by 40 foot slab covers 1,200 square feet, and in 2026 an installed slab runs about 6 to 12 dollars per square foot. That puts the finished job in the range of 7,200 to 14,400 dollars, with most standard pours landing near 8 to 10 dollars per square foot.
Where you fall in that range depends mostly on thickness, reinforcement, finish, and your region. A plain 4 inch slab with a broom finish sits at the bottom; a 6 inch reinforced slab with a gravel base and vapor barrier sits at the top.
| Build spec | Per sq ft | 30x40 total |
|---|---|---|
| 4 in, basic broom finish | 6 to 7 dollars | 7,200 to 8,400 dollars |
| 5 in, mesh reinforced | 7 to 9 dollars | 8,400 to 10,800 dollars |
| 6 in, rebar + gravel base | 9 to 12 dollars | 10,800 to 14,400 dollars |
To turn your own thickness and finish into a firm number, enter the dimensions in the concrete slab calculator and it returns yards, bags and an estimated cost.
How much concrete a 30x40 slab needs by thickness
Thickness drives the material cost more than anything else. Volume is length times width times thickness in feet, divided by 27 to get cubic yards. For 1,200 square feet, a 4 inch slab works out to about 14.8 cubic yards, and a 6 inch slab to about 22.2 cubic yards.
Cubic yards = 30 x 40 x (thickness in ÷ 12) ÷ 27Every extra inch across the full footprint adds roughly 3.7 cubic yards, so moving from 4 to 6 inches is about 50 percent more concrete. Order 10 to 15 percent over the calculated volume for waste and an uneven subgrade.
| Thickness | Cubic yards | +10% waste | Cubic meters |
|---|---|---|---|
| 4 in | 14.8 | 16.3 | 12.5 |
| 5 in | 18.5 | 20.4 | 15.6 |
| 6 in | 22.2 | 24.4 | 18.7 |
Labor versus materials on a 1,200 square foot pour
On a slab this size, labor and materials split fairly evenly. Labor is typically 40 to 50 percent of the total, and materials make up the rest. Installers charge about 3 to 5 dollars per square foot for forming, placing, finishing and curing.
Ready-mix concrete itself runs roughly 125 to 165 dollars per cubic yard delivered in 2026, so the raw concrete for a 4 inch pour is about 1,850 to 2,450 dollars before reinforcement. A truck holds 8 to 10 yards, so a 4 inch slab is usually two loads.
Because the crew forms and finishes the same 1,200 square feet regardless of depth, going thicker raises the material share while labor stays nearly flat. That is why a 6 inch slab often costs only 25 to 35 percent more overall, not 50 percent.
Add-ons that change the price: rebar, gravel and prep
The base slab is only part of the bill. The extras below are where two 30x40 quotes drift apart, and skipping the structural ones to save money is usually a false economy on a slab you want to last.
| Add-on | Cost per sq ft | 30x40 total |
|---|---|---|
| Rebar or wire mesh | 0.20 to 0.50 dollars | 240 to 600 dollars |
| Gravel base | 1 to 2 dollars | 1,200 to 2,400 dollars |
| Grading and site prep | varies | 500 to 2,000 dollars |
| Vapor barrier | 0.50 to 0.80 dollars | 600 to 960 dollars |
Reinforcement matters most once you pass 4 inches, since rebar controls cracking on a slab that carries vehicles or a building. A compacted gravel base under the slab is what keeps it from settling, so most contractors treat both as standard rather than optional.
What thickness a 30x40 slab should be
Match the thickness to the load. A patio, shed floor or light storage slab is fine at 4 inches. A garage, workshop or the base for a 30x40 metal building should be 5 to 6 inches, and a driveway that sees delivery trucks wants 6 inches with rebar.
The premium buys lifespan as much as strength: a 4 inch slab commonly lasts 15 to 20 years, while a properly based 6 inch slab reaches 25 to 30 years or more. If you are unsure how deep to pour, the guide on how thick a concrete slab should be maps thickness to use.
For a garage or building pad specifically, edge thickening and slab reinforcement change the math, which the note on garage slab thickness covers before you lock in a spec.
How region and finish move your final number
Location is a large swing. In the Midwest and South a 30x40 slab can land near 5 to 6 dollars per square foot, while coastal and Northeast markets often run 20 to 40 percent higher for the same spec, pushing a plain slab toward the top of the range.
Finish is the other lever. A broom finish is the cheapest and most common; a smooth trowel finish costs a little more, and stamped or colored concrete can add several dollars per square foot on top of the base price.
Because those factors compound, a written per-yard and per-square-foot quote from a local contractor beats any national average. To sanity check a bid before you sign, run your slab through the concrete slab calculator for a materials and cost baseline to compare against.
Frequently asked questions
How much does a 30x40 concrete slab cost?
How many yards of concrete for a 30x40 slab?
Is a 30x40 slab cheaper at 4 inches or 6 inches?
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How long does it take to pour a 30x40 slab?
References
- Concrete slab (Wikipedia)
- ACI 332: Residential Concrete Code
- NRMCA: Ready Mixed Concrete
- QUIKRETE Concrete Mix (spec sheet)