Concrete Slab: The Complete Guide
A concrete slab is a flat, poured layer of concrete that serves as a floor, a patio, a base for a structure, or a foundation. It is the most common form concrete takes around a home, from the pad under a shed to the ground floor of a house. Whether you are pricing a job, planning a pour, or ordering the concrete, a few numbers and decisions come up every time. This guide ties them together and links to the detail on each.
What a concrete slab is
At its simplest, a slab is concrete placed in a form over a prepared base and finished flat. What changes from one slab to the next is the thickness, the reinforcement inside it, and the base underneath, all chosen to match the load it will carry. A garden path and a garage floor are both slabs, but they are built to very different specs.
The decisions every slab comes down to
Planning a slab means settling a handful of questions in order.
- How much will it cost? A slab runs about $5 to $9 per square foot installed. See prices by size and what drives them.
- How thick should it be? Four inches for patios and sheds, 5 to 6 for driveways and garages. See the right thickness for your project.
- How much concrete do I order? Length times width times thickness, divided by 27 for cubic yards. See the formula and a size chart.
- What goes inside it? Rebar or wire mesh, plus a vapor barrier and gravel base. See sizes, spacing, and placement.
- How do I pour it? Lay out, base, forms, reinforce, pour, finish, cure. See the step-by-step guide.
- Is it a foundation? A slab-on-grade is both floor and foundation. See how slab foundations work.
Slab, pad, or foundation
The words overlap, so it helps to keep them straight. A slab is any flat poured concrete surface. A pad usually means a small freestanding slab, like the base for a shed, hot tub, or air conditioner. A slab foundation is a structural slab that carries a building, built with thickened edges and reinforcement to code. They are all concrete slabs, just sized and specced for the job.
Getting the numbers right
Almost every slab decision comes back to volume, because that sets both your concrete order and a big part of the cost. Measure the length, width, and thickness, convert to the same units, and you can price the job, order the right amount, and check a contractor's quote. The concrete slab calculator does that math for you, returning the cubic yards, bag counts, and a waste allowance from your dimensions, and the concrete slab cost calculator turns it into a dollar estimate. Pouring a flat interior floor rather than a foundation slab? Our concrete floor guide covers finishes, cost, and how thick to pour one.
Explore the concrete slab guides
Use the guides below to go deep on any part of a slab project, from pricing to pouring.
- Concrete Slab CostA concrete slab costs about $5 to $9 per square foot installed in 2026. See prices by slab size, what drives the cost up, and how to estimate your own pour.
- Concrete Slab ThicknessMost concrete slabs are 4 inches thick, but driveways, garages, and load-bearing slabs need 5 to 6 inches. See the right slab thickness for every project.
- How to Pour a Concrete SlabLearn how to pour a concrete slab in seven steps: layout, base, forms, reinforcement, pouring, finishing, and curing. A clear DIY guide with the key numbers.
- Concrete Slab FoundationA concrete slab foundation is a slab-on-grade that sits directly on the ground. See how monolithic and stem-wall slabs work, and slab vs crawl space vs basement.
- How Much Concrete for a SlabFigure out how much concrete a slab needs: multiply length by width by thickness in feet, then divide by 27 for cubic yards. See the formula, a chart, and bag counts.
- Rebar & ReinforcementWhat goes in and under a concrete slab: rebar or wire mesh for strength, a vapor barrier for moisture, and a gravel base. See sizes, spacing, and placement.
Frequently asked questions
What is a concrete slab?
A flat, poured layer of concrete used as a floor, patio, equipment pad, or foundation. Thickness and reinforcement are matched to the load it will carry.
How much does a concrete slab cost?
About $5 to $9 per square foot installed in 2026, with most standard 4-inch slabs near $7. Pouring it yourself can roughly halve that.
How thick should a concrete slab be?
Four inches for patios, walkways, and sheds. Five to six inches for driveways, garages, and anything carrying heavy loads.
How much concrete do I need for a slab?
Multiply length by width by thickness in feet, then divide by 27 for cubic yards. A 10 by 10 foot, 4-inch slab needs about 1.25 yards.