Concrete Slab / Pad Calculator
Estimate the exact amount of concrete you need for any rectangular or square slab project, including volume, bags, and cost.
1. Enter Slab Dimensions
Select your unit system to begin.
2. Get Results
Your results will appear here.
Enter dimensions and press Calculate.
Related Tools for Your Project
Guide to Calculating Concrete for Slabs & Pads
Calculating the right amount of concrete for a slab is crucial for the success of projects like patios, shed foundations, driveways, or floorings. Using too little can compromise the structure, while ordering too much is a waste of money. This calculator simplifies the process, but understanding the details can help you plan better. For a complete overview, read our comprehensive guide on calculating concrete.
Key Considerations for Slab Calculation:
- Uniform Thickness: Ensure your excavated area has a consistent, level depth. An uneven base is the most common reason for inaccurate estimates. Our calculator assumes a uniform thickness across the entire slab.
- Waste Factor: It is standard practice to add a 5-10% waste factor to your final volume. This accounts for spillage, over-excavation, and the small amount of concrete that will remain in the truck or mixer.
- Reinforcement: If you are using rebar or wire mesh, their volume is typically negligible and does not need to be subtracted from the total concrete volume for estimation purposes.
Frequently Asked Questions (FAQ)
What's the difference between a slab and a pad?
Generally, the terms are used interchangeably. "Slab" often refers to larger areas like floors or driveways, while "pad" might be used for smaller bases, such as for an AC unit or a small shed. The calculation method is identical for both.
How thick should my concrete slab be?
It depends on the load it will support:
- 4 inches (0.33 ft) is standard for patios, sidewalks, and shed foundations.
- 5-6 inches (0.42-0.5 ft) is recommended for driveways and garage floors that will support cars and light trucks.
For a deeper understanding of how thickness and other dimensions affect the total volume, check out our detailed concrete calculation guide.