How Thick Should a Concrete Slab Be?

Concrete thickness depends on what the slab needs to support. Too thin and it will crack; thicker than needed wastes material and money. Here are the standard thicknesses for every common project.

Thickness by slab type

Slab type	Minimum	Recommended	PSI
Sidewalk / walkway	3.5”	4”	3,000
Residential patio	3.5”	4”	3,000–3,500
Garage floor	4”	5”–6”	3,500–4,000
Driveway (cars)	4”	5”	4,000
Driveway (trucks/RVs)	5”	6”	4,000–4,500
Basketball/tennis court	4”	5”–6”	4,000
Workshop / shed floor	3.5”	4”	3,000
Pool deck	4”	4”	3,500

Gravel base requirements

Always place concrete over a compacted gravel base:

Slab use	Gravel base depth
Patio, sidewalk	4” compacted
Garage floor	4”–6” compacted
Driveway	4”–6” compacted
Heavy-duty	6”–8” compacted

Never pour concrete on soft, unstable, or organic soil.

Reinforcement guidelines

Slab	Reinforcement
Small patio (under 100 sq ft)	Fiber additive or none
Standard patio / sidewalk	6×6 wire mesh or fiber
Garage floor	#3 rebar @ 18” centers
Driveway	#4 rebar @ 18” centers
Structural slab	Engineer-specified rebar

Concrete quantities at different thicknesses

Coverage per cubic yard:

Thickness	Coverage per cu yd
3”	108 sq ft
3.5”	92 sq ft
4”	81 sq ft
5”	65 sq ft
6”	54 sq ft

Use the Concrete Calculator with your exact dimensions to get bags or ready-mix yards.

Pro tips

Add control joints every 8–12 feet to direct cracking
Cure properly — keep the slab moist for 3–7 days after pouring
Don’t pour in freezing temperatures — concrete won’t hydrate properly below 40°F
Slope for drainage — minimum ¼ inch per foot away from structures

Frequently Asked Questions

How thick should a concrete driveway be?

Residential driveways should be 4 inches thick at minimum, 5–6 inches for heavier vehicles like RVs or trucks. Use 4,000 PSI concrete and place it over a 4-inch compacted gravel base.

How thick should a concrete patio be?

A residential patio slab should be 4 inches thick. This is adequate for foot traffic, patio furniture, and grills. Increase to 5 inches if you plan to park a car on it.

How thick should a garage slab be?

A garage floor should be at least 4 inches thick for normal vehicles, or 5–6 inches for heavy trucks or storage. Include fiber reinforcement or rebar on a 4-inch gravel base.

Does a concrete slab need rebar?

Patios and small slabs can use fiber reinforcement or wire mesh. Driveways and load-bearing slabs benefit from #3 or #4 rebar on 18-inch centers. Thicker slabs (5"+) should always have rebar.

How many bags of concrete do I need for a 4-inch slab?

At 4 inches thick, 1 cubic yard covers 81 square feet. For a 10×10 ft patio (100 sq ft): 100 ÷ 81 = 1.23 cubic yards = about 56 bags of 80 lb concrete mix. Use our Concrete Calculator for exact numbers.