How Thick Should a Concrete Slab Be?
Most patios, sidewalks and shed floors are poured 4 inches thick. Driveways and slabs that carry cars or heavy equipment are commonly 5–6 inches. Structural slabs and footings follow your local code or an engineer's design.
Typical thickness by project
| Project | Common thickness | Concrete per 100 sq ft |
|---|---|---|
| Sidewalk, patio, walkway | 4 in | 1.23 cu yd |
| Shed or playhouse floor | 4 in | 1.23 cu yd |
| Hot tub pad | 4–6 in | 1.23–1.85 cu yd |
| Driveway (cars) | 5–6 in | 1.54–1.85 cu yd |
| Garage floor, RV pad | 5–6 in | 1.54–1.85 cu yd |
Thickness is only half the story
A slab is only as strong as what's under it. A compacted gravel base (typically around 4 inches) spreads loads and drains water; reinforcement such as wire mesh, rebar or fiber helps control cracking; and control joints cut at regular spacing give the slab a place to crack neatly. A thick slab poured on soft, uncompacted soil will still crack.
Each inch matters for the order
Going from 4 to 5 inches adds 25% more concrete; 4 to 6 inches adds 50%. Put your exact dimensions into the concrete calculator and compare thicknesses before you order. Check edges: many slabs are thickened at the perimeter, which adds volume.