Concrete Slab Calculator
Estimate concrete for a slab — patio, garage, or shed floor. Enter length, width, and thickness to get cubic yards and 40/60/80 lb bag counts, with a cost estimate.
How thick should a concrete slab be?
| Use | Typical thickness |
|---|---|
| Patio / walkway | 4 in |
| Shed floor | 4 in |
| Driveway | 4–5 in |
| Garage floor | 5–6 in |
What the thickness number changes
Thickness changes the volume directly. On the same slab footprint, increasing thickness from 4 in to 5 in adds about 25% more concrete. Increasing from 4 in to 6 in adds about 50% more.
Run the estimate for each thickness you are considering before you order. The calculator updates both cubic yards and bag counts, so you can compare the material difference without changing the rest of the project dimensions.
Estimating an irregular slab
This calculator assumes a rectangular slab. For an L-shape, notch, or slab made from multiple rectangular areas, split the project into rectangles, estimate each rectangle separately, and add the cubic-yard totals together.
If one part of the slab is thicker than another, estimate each section at its own thickness and add the results. Treat the total as a planning estimate and confirm the final quantity with your supplier before buying materials.
Common slab sizes (at 4 in)
| Slab | Concrete |
|---|---|
| 8 × 8 ft | ~0.79 cu yd |
| 10 × 10 ft | ~1.23 cu yd |
| 12 × 12 ft | ~1.78 cu yd |
| 24 × 24 ft (garage) | ~7.11 cu yd |
Related calculators
Concrete calculator (all shapes) · Concrete footing calculator · Gravel base calculator
FAQ
How thick should a concrete slab be?
4 in for patios/walkways; 5–6 in for driveways and garage floors.
How much concrete for a 12×12 slab?
About 1.78 cu yd (48 cu ft) at 4 inches. Add 5–10% for waste.