Concrete Slab Cost and Thickness Guide for DIY Projects
Slab thickness and volume drive both strength and cost. Get them right and your patio, shed pad, or driveway lasts for decades.
A concrete slab needs enough thickness for its load and enough volume calculated correctly so you order the right amount. Under-order and you risk a cold joint mid-pour; over-order and you pay for concrete you cannot use. This guide covers both.
How thick should the slab be?
Thickness depends on what the slab carries. Use these common minimums as a starting point and follow local code for anything structural.
| Use | Typical thickness |
|---|---|
| Garden or shed floor | 3.5 – 4 in |
| Patio or walkway | 4 in |
| Standard driveway (cars) | 4 – 5 in |
| Driveway with heavy vehicles | 5 – 6 in |
| Garage floor | 4 – 6 in |
Estimating the volume
Volume equals length times width times thickness, all in the same units. Convert thickness in inches to feet by dividing by 12. A 10 by 12 foot patio at 4 inches is 10 × 12 × (4 / 12) = 40 cubic feet. Since concrete is sold by the cubic yard (27 cubic feet), that is 40 / 27 = about 1.5 cubic yards. Always add 5 to 10 percent for spillage, uneven subgrade, and over-excavation.
Bags versus ready-mix
Bagged concrete makes sense for small pours. An 80-pound bag yields about 0.6 cubic feet, so the patio above needs roughly 40 / 0.6 = 67 bags. That is a lot of mixing, which is why ready-mix delivery is usually more economical once you pass about a cubic yard. Most suppliers have a minimum load and a short-load fee below a full truck.
2026 cost ranges
| Option | Typical 2026 cost |
|---|---|
| Ready-mix concrete | $140 – $180 per cubic yard |
| 80 lb bag | $5 – $8 each |
| DIY slab, materials only | $5 – $10 per sq ft |
| Professionally poured slab | $8 – $18 per sq ft |
Don't forget the base and reinforcement
A slab is only as good as what sits under it. Plan for 4 to 6 inches of compacted gravel base for drainage and stability, and add wire mesh or rebar for driveways and larger slabs. These add to your material list, so estimate the gravel separately.
Practical ordering tips
- Round up to the nearest quarter yard when ordering ready-mix.
- Have all forms, base, and reinforcement ready before the truck arrives.
- Order a little extra rather than risk running short mid-pour.
- Plan your pour for mild weather and give the slab time to cure.