Concrete Slab Calculator

Q: How much does a concrete slab cost?

A concrete slab costs $6 to $12 per square foot installed, with most homeowners paying $7 to $10 per square foot. A typical 20 ft by 20 ft garage slab (400 sq ft) runs $2,800 to $4,000 installed. Concrete patios sit at the low end and heavier garage slabs at the top. Decorative finishes (stamped, stained, polished) add 30 to 100 percent.

Q: How thick should a concrete slab be?

Use 4 inches for patios, walkways, and shed floors. Use 5 to 6 inches for driveways and garage floors with passenger vehicles. Use 6 to 8 inches for heavy loads (RVs, trucks, machinery) or if your soil is poor. The thicker the slab, the more concrete and the higher the cost, but going thinner than your use case is the most common cause of cracking.

A concrete slab costs $6.00 to $12 per sq ft installed, with most homeowners landing at $7.00 to $10 per sq ft. A typical 20 ft × 20 ft garage slab (400 sq ft, 4 in thick) runs about $2,800 to $4,000 installed, or $1,000 to $1,800 in materials if you pour it yourself. Enter your dimensions below to get cubic yards of concrete, gravel base, and total cost.

Estimated total—

Your slab

Length Width Thickness (in)

Unit

feetmeters

Price assumptions

Concrete ($/cubic yd, delivered) Gravel base ($/cubic yd) Reinforcement ($/sq ft) Installation labor ($/sq ft)

Defaults & assumptions

Defaults: a typical 20 ft × 20 ft garage slab (400 sq ft, 4 in thick) and US national average rates. Adjust the rates above to match local quotes. Set labor to 0 for a DIY materials estimate. Set reinforcement to 0 if you don’t need mesh.

Enter your slab dimensions above to see results.

Concrete slab cost per square foot

A concrete slab has two materials you buy by the cubic yard and two you price per square foot. The biggest line item is the concrete itself, $120 to $150 per cubic yard delivered; small deliveries (under 3 to 4 yards) often add a short-load fee. Underneath the slab goes a 4 in to 6 in compacted gravel base, another $30 to $45 per cubic yard. Reinforcement (wire mesh or rebar) adds $0.30 to $1.50 per sq ft of material, and installation labor runs $3.00 to $6.00 per sq ft for forming, pouring, and finishing a basic broom-finish slab. Sum it: about $6.00 to $12 per sq ft installed, with decorative finishes (stamped, stained, polished) adding 30 to 100 percent on top.

Typical concrete slab cost by size (US averages, 4" thick, installed)
Slab size	Materials only (DIY)	Professionally installed
120 sq ft	$300 to $700	$750 to $1,500
200 sq ft	$500 to $1,000	$1,300 to $2,400
400 sq ft	$900 to $1,800	$2,800 to $4,000
600 sq ft	$1,300 to $2,700	$4,200 to $6,000
1,000 sq ft	$2,100 to $4,500	$7,000 to $10,000

How the calculator works

Concrete volume is length × width × thickness in feet (thickness inches ÷ 12), converted to cubic yards (÷ 27), then bumped by your waste percentage to cover spillage and short pours. Add 5 to 10 percent for waste; slabs are unforgiving since you can’t come back for a half-yard. Gravel base is a 4 in compacted layer over the slab area, converted to cubic yards and tons. Costs are quantities times your local rates, with labor priced per square foot the way contractors quote it. Excludes: site prep beyond the gravel base, re-turfing afterward (see our sod calculator), and any necessary permits. Price ranges reflect published US averages from national cost guides (Angi, HomeGuide, HomeAdvisor, 2026).

Concrete slab cost FAQ

How much does a concrete slab cost?

A concrete slab costs $6.00 to $12 per sq ft installed, with most homeowners paying $7.00 to $10 per sq ft. A typical 20 ft by 20 ft garage slab (400 sq ft) runs $2,800 to $4,000 installed. Concrete patios sit at the low end and heavier garage slabs at the top. Decorative finishes (stamped, stained, polished) add 30 to 100 percent.

How many cubic yards of concrete do I need for a slab?

Multiply length by width by thickness in feet (thickness inches ÷ 12), then divide by 27. A 20 ft by 20 ft slab 4 in thick needs about 4.9 cubic yards of concrete before waste. Add 5 to 10 percent for spillage and over-excavation: order about 5.5 cubic yards to be safe.

How thick should a concrete slab be?

Use 4 in for patios, walkways, and shed floors. Use 5 in to 6 in for driveways and garage floors with passenger vehicles. Use 6 in to 8 in for heavy loads (RVs, trucks, machinery) or if your soil is poor. The thicker the slab, the more concrete and the higher the cost, but going thinner than your use case is the most common cause of cracking.

Do I need rebar in a concrete slab?

Wire mesh reinforcement is standard in most residential slabs because it controls hairline cracking without adding much cost. Rebar (steel reinforcing bar) goes in heavier slabs and high-load areas. Fiber mesh mixed into the concrete is the cheapest option and works for shed floors and basic patios. For a typical residential slab, mesh at $0.30 to $0.50 per sq ft is the most common choice.