Standard: 4" for patios, 5-6" for driveways
Average: $125-$150 per cubic yard
How to Calculate Concrete Slab Volume
Rectangular Slab
Formula: Volume = Length × Width × Thickness
Example (20' × 20' × 4"):
- Area: 20 × 20 = 400 sq ft
- Thickness: 4" = 0.33 feet
- Volume: 400 × 0.33 = 133.3 cubic feet
- Cubic Yards: 133.3 ÷ 27 = 4.94 cubic yards
Circular Slab
Formula: Volume = π × r² × Thickness
Where r = radius, π = 3.14159
Example (12' diameter × 4"):
- Radius: 12 ÷ 2 = 6 feet
- Area: π × 6² = 113.1 sq ft
- Thickness: 4" = 0.33 feet
- Volume: 113.1 × 0.33 = 37.3 cubic feet
- Cubic Yards: 37.3 ÷ 27 = 1.38 cubic yards
Recommended Slab Thickness
- Sidewalks: 3-4 inches
- Patios: 4-5 inches
- Driveways: 5-6 inches
- Garage Floors: 6 inches
- Foundation Slabs: 6-8 inches
Cost Estimation
- Concrete: $125-$150 per cubic yard
- Delivery: $50-$100 per truck
- Pump Service: $200-$400 (if needed)
- Reinforcement: $0.50-$1.50 per sq ft
About This Calculator
Concrete Slab Calculator - Estimate Concrete for Slabs & Footings
Calculate concrete volume for rectangular and circular slabs. Get accurate estimates in cubic yards, cubic meters, and number of bags needed with cost calculations.
How to Use This Calculator
- Select Shape: Choose rectangle/square or circle
- Enter Dimensions: Input length, width, or diameter in feet
- Set Thickness: Enter slab thickness (inches or feet)
- Add Price (optional): Enter cost per cubic yard for estimate
- Get Results: See concrete volume, bags, and cost
Concrete Slab Volume Formulas
Rectangular Slab
Formula:
Volume = Length × Width × ThicknessExample (20' × 20' × 4"):
- Area: 20 × 20 = 400 sq ft
- Thickness: 4" = 0.33 feet
- Volume: 400 × 0.33 = 133.3 cubic feet
- Cubic Yards: 133.3 ÷ 27 = 4.94 cubic yards
- Add 10% waste: 4.94 × 1.10 = 5.4 cubic yards
Circular Slab
Formula:
Volume = π × r² × ThicknessWhere r = radius, π = 3.14159
Example (12' diameter × 4"):
- Radius: 12 ÷ 2 = 6 feet
- Area: π × 6² = 113.1 sq ft
- Thickness: 4" = 0.33 feet
- Volume: 113.1 × 0.33 = 37.3 cubic feet
- Cubic Yards: 37.3 ÷ 27 = 1.38 cubic yards
- Add 10% waste: 1.38 × 1.10 = 1.5 cubic yards
Recommended Slab Thickness
| Application | Minimum | Recommended |
|---|---|---|
| Sidewalks | 3 inches | 4 inches |
| Patios | 3 inches | 4-5 inches |
| Driveways | 4 inches | 5-6 inches |
| Garage Floors | 5 inches | 6 inches |
| Foundation Slabs | 4 inches | 6-8 inches |
Concrete Bag Coverage
- 80lb Bag: 0.60 cubic feet (0.022 cubic yards) - ~54 bags per cubic yard
- 60lb Bag: 0.45 cubic feet (0.017 cubic yards) - ~72 bags per cubic yard
- 40lb Bag: 0.30 cubic feet (0.011 cubic yards) - ~108 bags per cubic yard
Cost Considerations
- Ready-Mix Concrete: $125-$150 per cubic yard
- Delivery Fee: $50-$100 per truck
- Pump Service: $200-$400 (if needed for access)
- Wire Mesh: $0.30-$0.50 per sq ft
- Rebar: $0.50-$1.50 per sq ft
- Labor: $50-$150 per hour
Reinforcement Guidelines
- 4" Slabs: Wire mesh or #3 rebar on 18-24" grid
- 5-6" Slabs: #4 rebar on 12-18" grid
- Driveways: Always use reinforcement
- Garage Floors: #4 rebar recommended
Common Slab Sizes
| Project | Size | Thickness | Volume (cy) |
|---|---|---|---|
| Small Patio | 10' × 10' | 4" | 1.2 |
| Large Patio | 20' × 15' | 4" | 3.7 |
| Single Car Garage | 12' × 20' | 6" | 5.3 |
| Double Car Garage | 24' × 24' | 6" | 12.8 |
| Driveway | 20' × 20' | 5" | 6.2 |
Installation Tips
- Prepare subgrade - level and compact soil
- Add gravel base (4-6" for slabs)
- Install vapor barrier for indoor slabs
- Place reinforcement on chairs (not on ground)
- Order 5-10% extra concrete
- Pour in cool weather if possible
- Use control joints for crack control
Curing Recommendations
- Initial Set: 24-48 hours
- Foot Traffic: 3-7 days
- Light Vehicles: 7 days
- Full Strength: 28 days
Frequently Asked Questions
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