How Thick Should Concrete Be? (By Project Type)

Patios need 4 inches. Driveways need 5-6 inches. Garage floors need 4-6 inches. The right thickness depends on what the concrete will support—foot traffic, passenger vehicles, or heavy trucks.

Getting thickness wrong leads to cracking and premature failure. This guide covers every common residential project.

Master Thickness Reference

Here's what professionals recommend for each project type:

Project	Minimum	Recommended	Heavy Use
Patio	4"	4"	5"
Sidewalk	4"	4"	4"
Shed floor	4"	4"	5"
Driveway (cars)	4"	5"	6"
Driveway (trucks/RV)	5"	6"	8"
Garage floor	4"	4-6"	6"
Basement floor	3"	4"	4"
Footings	8"	8-12"	Per code
Foundation walls	8"	8-10"	Per code

"Minimum" means it might work but risks problems. "Recommended" is what professionals typically install. "Heavy use" is for above-average loads.

Thickness by Project (Detailed)

Patios

Recommended: 4 inches

Patios support foot traffic and patio furniture—relatively light loads spread over large areas. Four inches is standard and sufficient for nearly all residential patios.

When to go thicker (5"):

• Hot tub pad (concentrated load)
• Heavy stone furniture
• Potentially driving a riding mower across it

Use our patio calculator to determine quantities.

Sidewalks

Recommended: 4 inches

Sidewalks handle walking traffic only. Four inches is standard for both private and public sidewalks. There's rarely reason to go thicker.

Exception: If utility trucks will occasionally drive across the sidewalk to access your yard, reinforce with wire mesh—but 4 inches is still adequate.

Driveways

Recommended: 5-6 inches

Driveways support vehicles, which create point loads and dynamic stress. This is where thickness matters most—and where cutting corners causes the most problems.

Vehicle Type	Minimum Thickness
Passenger cars only	5 inches
Trucks, SUVs	5-6 inches
Heavy trucks, RVs	6-8 inches
Commercial vehicles	8+ inches

Common mistake: Pouring a 4-inch driveway to save money. The concrete costs less, but a cracked driveway costs far more to replace than the incremental cost of the extra inch.

For detailed driveway guidance, see our driveway thickness guide or use our driveway calculator.

Garage Floors

Recommended: 4-6 inches

Garage floors support parked vehicles (static load), but also need to handle fluid spills, dropped tools, and decades of use.

Garage Use	Thickness
Light storage, no vehicles	4 inches
Standard residential (cars)	4-5 inches
Workshop with equipment	5-6 inches
Heavy vehicles or lifts	6+ inches

If you're installing a car lift, consult the lift manufacturer for floor requirements—some require 6"+ with specific reinforcement.

Shed Floors

Recommended: 4 inches

Most sheds store lawn equipment, tools, and seasonal items—nothing that requires extra thickness. Four inches is standard.

Go thicker if:

• Storing heavy equipment (tractors, ATVs)
• Converting to workshop with heavy machinery
• Supporting unusual point loads

Footings and Foundations

Recommended: Per local building code

Footings and foundations are structural elements governed by building codes. Thickness varies by:

• Soil bearing capacity
• Building loads
• Frost depth
• Local requirements

Typical residential:

• Footings: 8-12 inches thick, extending below frost line
• Foundation walls: 8-10 inches thick

Always check local code or consult a professional for structural concrete. These aren't DIY guesses—they're engineered requirements.

Why Thickness Matters

Load Distribution

Concrete distributes weight downward in a cone pattern. Thicker slabs spread loads over larger soil areas, reducing stress on any single point.

A 4-inch slab under a car tire concentrates stress; a 6-inch slab spreads that same load over roughly 50% more soil area.

Flexure Resistance

When loads aren't centered (like a car driving near an edge), concrete bends slightly. This creates tension on the bottom surface—where cracking starts.

Thicker concrete resists bending better. The relationship isn't linear: a 6-inch slab is significantly stronger in flexure than a 4-inch slab, not just 50% stronger.

Reinforcement Depth

Rebar and wire mesh need to be positioned at mid-depth. In a 4-inch slab, that's 2 inches from each surface—just enough room. Thicker slabs give more margin for proper positioning.

For reinforcement guidance, see when to use rebar.

Cost Impact of Thickness

Going thicker costs more—but how much more?

Thickness	Yards per 100 sqft	Cost per 100 sqft
4 inches	1.23 yards	~$185 (materials)
5 inches	1.54 yards	~$230 (materials)
6 inches	1.85 yards	~$280 (materials)

The math: Going from 4" to 6" increases material cost by about 50%. For a 400-sqft driveway, that's roughly $380 extra in materials—cheap insurance against cracking.

For full project pricing, see concrete cost per square foot.

What Happens If Concrete Is Too Thin

Undersized concrete fails predictably:

Cracking: Loads exceed the concrete's flexural capacity. Cracks start at the bottom (tension side) and propagate upward.

Spalling: Surface breaks away, especially at edges and around cracks.

Settlement: Thin slabs can't bridge soft spots in the subgrade. Sections sink independently.

Premature failure: A 4-inch driveway might crack within 2-5 years. A 5-6 inch driveway lasts 25-30 years.

The expensive lesson: Replacing a failed slab costs far more than pouring it correctly the first time. You pay for demo, removal, disposal, and full installation.

Factors That Require Extra Thickness

Consider going thicker than standard if:

• Poor soil conditions: Expansive clay or loose fill doesn't provide stable support
• No gravel base: Concrete directly on soil needs more thickness for margin
• Minimal reinforcement: If you're skipping rebar (not recommended for driveways), thicker helps
• Frost heave risk: In cold climates, thicker slabs resist heaving better
• Point loads: Hot tubs, heavy equipment, or vehicle lifts concentrate stress

Use a Calculator for Quantities

Once you know the right thickness, calculate how much concrete you need:

Formula: Length × Width × Thickness (in feet) ÷ 27 = cubic yards

Example: 20×20 driveway at 5"

• 20 × 20 × 0.42 ÷ 27 = 6.2 cubic yards

Use our concrete calculator or slab calculator to skip the math. For step-by-step calculation guidance, see how to calculate concrete.

Frequently Asked Questions

Is 4 inches of concrete enough for a driveway?

No—4 inches is too thin for vehicle traffic. Passenger cars create stress that 4-inch concrete can't reliably handle long-term. Use 5 inches minimum for cars, 6 inches if you have trucks, SUVs, or expect heavier vehicles.

Does thicker concrete last longer?

Yes, up to a point. Thicker concrete handles loads better, resists cracking, and tolerates subgrade imperfections. A properly installed 5-6 inch driveway should last 25-30 years; a 4-inch driveway may fail in 5-10 years.

What happens if my concrete is too thin?

Thin concrete cracks under loads it can't support. Cracks start at the bottom and spread upward. Once cracking begins, it accelerates. Thin slabs also settle into soft spots rather than bridging them. The only fix is usually replacement.

How thick should concrete be over rebar?

Rebar should have at least 1.5-2 inches of concrete cover (called "clear cover") on all sides. In a 4-inch slab, rebar sits at 2" depth—barely enough. Thicker slabs allow better positioning and more protective cover.

Key Takeaways

• Patios and sidewalks: 4 inches
• Driveways: 5-6 inches minimum
• Garage floors: 4-6 inches depending on use
• Footings/foundations: Check local code
• Going too thin costs more in the long run than doing it right

Use our concrete calculator after determining thickness. For more detail, see our complete concrete guide or browse all concrete guides.