Concrete Slab Calculator
Material Estimates
Total Volume:
0 Cubic Yards
Total Cubic Feet:
0 ft³
80lb Bags Needed:
0 Bags
60lb Bags Needed:
0 Bags
Estimated Cost (80lb bags):
0
*Includes a 10% waste safety margin.
How to Calculate Concrete for a Slab
Planning a patio, driveway, or shed foundation requires accurate material estimation. Concrete is sold by volume (cubic yards) when delivered by truck, or by the bag (60lb or 80lb) for smaller DIY projects. This calculator helps you determine exactly how much premix you need to buy to avoid running out mid-pour.
The Concrete Formula
The basic formula for concrete volume is Length × Width × Thickness. However, since length and width are usually measured in feet and thickness in inches, unit conversion is necessary:
- Step 1: Convert thickness to feet (Thickness in inches ÷ 12).
- Step 2: Multiply Length (ft) × Width (ft) × Thickness (ft) to get Cubic Feet.
- Step 3: Divide Cubic Feet by 27 to get Cubic Yards (since there are 27 cubic feet in one cubic yard).
How Many Bags Do I Need?
Most hardware stores sell premix concrete (like Quikrete or Sakrete) in 60lb or 80lb bags. To calculate the bag count manually:
- 80lb Bag Yield: Approximately 0.60 cubic feet.
- 60lb Bag Yield: Approximately 0.45 cubic feet.
Pro Tip: Always add a 5-10% safety margin (waste factor) to account for spillage, uneven subgrade, or slight variations in slab thickness. Our calculator automatically includes a 10% buffer to ensure you have enough material.
Standard Slab Thickness Guidelines
- 4 Inches: Standard for sidewalks, patios, and non-weight bearing shed floors.
- 5-6 Inches: Recommended for driveways and garage floors to support vehicle weight.
- 6+ Inches: Heavy-duty applications or areas with poor soil conditions.