Concrete Slab Thickness Cheat Sheet

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Recommended thickness, strength, rebar, and base prep for every common slab — on one printable page

Pouring a slab too thin is the single most expensive mistake a DIYer makes — cracked patios and crumbling driveways almost always trace back to insufficient thickness or a weak base. This cheat sheet gives you the recommended thickness, concrete strength (PSI), reinforcement, and gravel base for the slabs people pour most often, plus a yardage coverage table so you order the right amount.

Recommended Thickness by Use

Application	Thickness	PSI	Gravel Base	Reinforcement
Walkway / sidewalk	4 in	3,000	4 in compacted gravel	Optional fiber or 6x6 mesh
Patio	4 in	3,000	4 in gravel	6x6 wire mesh
Shed / outbuilding floor	4 in	3,000-3,500	4 in gravel	6x6 mesh or #3 grid
Garage floor (cars)	4 in	3,500-4,000	4-6 in gravel	#3 rebar 18 in grid
Standard driveway (cars)	4 in	3,500-4,000	4-6 in gravel	#3-#4 rebar 18 in grid
Driveway (trucks / RV)	5-6 in	4,000	6 in gravel	#4 rebar 12-18 in grid
Workshop / pole barn	5-6 in	4,000	6 in gravel	#4 rebar 12 in grid
Footings / foundations	6-12 in	3,000-4,000	Undisturbed soil	#4-#5 rebar per plan

When in doubt, go one step thicker. The extra concrete is far cheaper than tearing out and re-pouring a failed slab.

Yardage Coverage (1 Cubic Yard)

Slab Thickness	1 cu yd covers	Per sq ft
4 in	81 sq ft	0.012 cu yd
5 in	65 sq ft	0.015 cu yd
6 in	54 sq ft	0.019 cu yd
8 in	40 sq ft	0.025 cu yd

Always order 5-10% extra for spillage, uneven subgrade, and over-excavation. Concrete is sold in whole or half yards.

Joints, Base & Curing Rules

Rule	Value	Notes
Control joint spacing	24-30x slab thickness	A 4 in slab = joints every 8-10 ft
Control joint depth	1/4 of slab thickness	1 in deep on a 4 in slab
Max joint panel	Keep panels near square	Avoid long thin rectangles
Vapor barrier	6-10 mil poly	Under all interior/heated slabs
Rebar cover	2-3 in from edges	Keep steel in the middle third
Cure time (foot traffic)	24-48 hrs	Full strength at 28 days

Quick Volume Estimator

Fill in your slab to estimate cubic yards: (length ft x width ft x thickness ft) / 27. Remember thickness in feet = inches / 12 (4 in = 0.33 ft).

Length

Width

Thickness

Square Footage

sq ft

Cubic Feet

cu ft

Cubic Yards (cu ft / 27)

cu yd

+ 10% Waste

cu yd

Order Total

cu yd

Project Notes & Local Frost Depth

Order the right amount the first time. Use the free Concrete Calculator at buildcalcpro.org to convert your slab dimensions into exact cubic yards and bag counts, then cross-check the thickness against this chart. Figures reflect typical residential practice and the IRC; always confirm footing depth and frost requirements with your local building department.