Concrete Slab Calculator
Estimate how much concrete you need for slabs, patios, driveways, garage floors, sidewalks, footings, and other flat concrete projects.
Project dimensions
Enter your slab dimensions and preferences.
How to Use the Concrete Calculator
Enter the length, width, and thickness of your concrete project. The calculator estimates the total volume in cubic feet and cubic yards, then adds your selected waste percentage. You can also enter a price per cubic yard to estimate material cost.
Common Concrete Slab Thicknesses
| Project Type | Common Thickness |
|---|---|
| Sidewalk or walkway | 4 inches |
| Patio slab | 4 inches |
| Garage floor | 4–6 inches |
| Driveway | 4–6 inches |
| Heavy vehicle pad | 6+ inches |
Example Concrete Estimate
For a 20 ft by 12 ft slab at 4 inches thick, the volume is about 80 cubic feet. Dividing by 27 gives roughly 2.96 cubic yards. With 10% waste, you would need about 3.26 cubic yards.
Should You Add Extra Concrete?
Yes. Most projects should include at least 5–10% extra concrete. Extra material helps account for uneven ground, spillage, measurement differences, and ordering safety. It is usually better to have slightly too much concrete than to run short during a pour.
Frequently Asked Questions
How many cubic feet are in a cubic yard?
There are 27 cubic feet in one cubic yard.
How many bags of concrete are in a cubic yard?
It depends on bag size. As a rough estimate, one cubic yard requires about 45 80-lb bags, 60 60-lb bags, or 90 40-lb bags.
How thick should a concrete slab be?
Many patios, sidewalks, and light-duty slabs are around 4 inches thick. Driveways, garages, and heavier-use slabs are often 4–6 inches or more.
Does this calculator include waste?
Yes. You can enter a waste percentage. A 5–10% waste allowance is common for many concrete projects.