How Thick Should a Concrete Slab Be? Patios, Pads and Driveways
Typical thicknesses for walkways, patios, shed pads and driveways, and how much more concrete a thicker slab takes.
Thickness is the biggest single decision in a concrete slab. Too thin and it cracks under load; too thick and you pay for concrete you didn’t need. For most home projects the answer is between 4 and 6 inches.
Typical thicknesses
| Project | Typical thickness |
|---|---|
| Walkways and garden paths | 4” |
| Patios | 4” |
| Shed and hot-tub pads | 4–6”, depending on the weight |
| Driveways for passenger cars | 4” minimum; many builders pour 5” |
| Driveways for heavy trucks or RVs | 5–6” |
Sources such as ConcreteNetwork put a residential driveway at a minimum of 4”, and 5–6” for heavier vehicles. Your local building department may set its own minimum for driveways and aprons, so check before you pour.
Thickness is only part of it
A thick slab on a poor base still cracks. What sits under the concrete matters just as much:
- A compacted gravel base, usually about 4”, gives the slab even support and drainage.
- Reinforcement (rebar or wire mesh) holds cracks tight if they form.
- Control joints, cut about a quarter of the slab’s depth, decide where cracks happen. Space them no more than 2–3 times the slab thickness in feet: about every 8–12 ft for a 4” slab.
- Thicken the edges where the slab carries vehicles, or where it meets soft ground.
How much more concrete a thicker slab takes
Cubic yards including 10% extra:
| Slab | 4” | 5” | 6” |
|---|---|---|---|
| 10 × 10 ft | 1.36 yd | 1.7 yd | 2.04 yd |
| 12 × 12 ft | 1.96 yd | 2.44 yd | 2.93 yd |
| 12 × 20 ft | 3.26 yd | 4.07 yd | 4.89 yd |
| 20 × 20 ft | 5.43 yd | 6.79 yd | 8.15 yd |
Going from 4” to 6” adds 50% more concrete. Thickness also eats into your height: a 6” slab on a 4” base needs a 10” dig below the finished surface.
Bags or a truck?
At 4” thick, around 80 square feet of slab uses about one cubic yard, or roughly 45 bags of 80 lb. Above that, most people order ready-mix. See How Many Bags of Concrete Do You Need? for bag tables, and How to Pour a Concrete Patio Slab for the whole job.
Try different thicknesses in the Concrete Slab & Footing Planner to see the concrete, rebar and base gravel for your slab.