Concrete Slab Calculator 2026
Instantly estimate the volume of concrete needed for your project. Calculate cubic yards, cubic meters, and bag counts for patios, driveways, and foundations with precision waste factor adjustments.
Slab Dimensions
Define the shape and size of your concrete pour
The longest dimension of the slab area.
The shorter dimension of the slab area.
Standard patios are 4″, driveways often 6″ or more.
Add 10% for standard spills/rough forms. Add 15-20% for complex shapes.
Material Profile
Volume, Bags, & Project Scale
Configure your slab dimensions and waste factor, then click Estimate Materials to view your concrete requirements.
Common Slab Dimensions
Standard volume estimates for typical residential concrete projects at 4 inches thickness.
| Project Type | Dimensions (ft) | Volume (yd³) | 80lb Bags (approx) |
|---|---|---|---|
| Small Patio | 10 x 10 | 1.23 | 56 |
| Walkway (3×10) | 3 x 10 | 0.37 | 17 |
| Shed Base (8×10) | 8 x 10 | 0.99 | 45 |
| Standard Driveway | 12 x 40 | 5.90 | 268 |
| Garage Floor (20×20) | 20 x 20 | 9.88 | 449 |
Concrete Estimation FAQ
Learn more about calculating volume, choosing between bags and ready-mix, and managing waste.
To calculate the volume of a rectangular slab, multiply the Length × Width × Thickness. Ensure all measurements are in the same unit (e.g., feet) before converting to cubic yards (divide by 27) or cubic meters.
For a 10×10 foot slab at 4 inches thick, the volume is approximately 1.23 cubic yards. This requires about 56 bags of 80lb concrete or 74 bags of 60lb concrete. Always add 10% for waste and spillage.
A standard waste factor is 10%. This accounts for spillage, over-digging, irregular forms, and finishing losses. For complex shapes or rough terrain, increase the waste factor to 15-20%.
For projects under 1 cubic yard, mixing bags is usually more convenient. For projects between 1 and 3 cubic yards, bags are possible but labor-intensive. For anything over 3-4 cubic yards, ordering a Ready-Mix truck is significantly faster and often more cost-effective.
Standard residential driveways should be at least 4 inches thick. If you expect heavy trucks or RVs, increase the thickness to 5 or 6 inches and ensure the sub-base is properly compacted.