Concrete Volume & Bags Calculator
Calculate exact cubic yards, cubic feet, and bagged concrete required for slabs, footings, steps, and driveways.
Dimensions & Specifications
Ready to order materials? Verify your dimensions against local building codes before ordering pre-mix trucks or bagged pallets.
How to Calculate Concrete Slab Volume
Concrete volume is measured in cubic yards (or cubic meters in metric regions). One cubic yard is equal to 27 cubic feet. To calculate the volume of a slab or driveway, multiply the length by the width to get the surface area, convert the thickness to consistent units, multiply to get volume, and add your waste factor.
Imperial: Volume (cu yds) = [Length (ft) × Width (ft) × (Thickness (in) / 12)] ÷ 27
Metric: Volume (m³) = Length (m) × Width (m) × (Thickness (cm) / 100)
Recommended Concrete Slab Thickness Guide
| Project Type | Standard Thickness | Recommended PSI | Reinforcement |
|---|---|---|---|
| Sidewalk / Garden Walkway | 3.5" to 4.0" (9-10 cm) | 3,000 PSI | Fiber mesh or #3 rebar |
| Backyard Patio | 4.0" (10 cm) | 3,500 PSI | 6x6 welded wire mesh |
| Residential Car Driveway | 4.5" to 5.0" (12-13 cm) | 4,000 PSI | #4 rebar on 18" grid |
| Heavy RV Pad / Garage Floor | 6.0" (15 cm) | 4,000+ PSI | #4 rebar on 12" grid |
Frequently Asked Questions
How many 80-lb bags of concrete do I need for a 10x10 slab at 4 inches thick?
For a 10x10 foot slab at 4 inches thick (100 sq ft), you need 1.23 cubic yards of concrete. With a recommended 10% waste allowance, you will need 62 bags of 80-pound concrete (or 82 bags of 60-pound concrete).
How many bags of concrete make 1 cubic yard?
One cubic yard equals 27 cubic feet. It takes 45 bags of 80-lb concrete, 60 bags of 60-lb concrete, or 90 bags of 40-lb concrete to make exactly 1 cubic yard.
How thick should a residential concrete slab be?
Standard residential walkways and patios are typically poured 4 inches thick (using 3000 to 3500 PSI mix). Car driveways should be 4 to 5 inches thick, while heavy RV pads and commercial slabs should be 6 inches thick with #4 rebar reinforcement.
How much does a cubic yard of concrete weigh?
Standard mixed wet concrete weighs approximately 150 lbs per cubic foot, which equals roughly 4,050 lbs (approx. 2.025 short tons) per cubic yard.