Concrete Volume & Bag Calculator
Rectangular Slab / Wall
Circular Column / Post Hole
80 lb bags
60 lb bags
40 lb bags
Estimation Results
Total Volume: Cubic Yards
Total Volume: Cubic Feet
Number of Bags Needed:
How to Use the Concrete Calculator
Calculating the exact amount of concrete needed for a DIY project is critical to avoid expensive overruns or, worse, running out mid-pour. This calculator determines the volume for slabs, footings, and columns while accounting for standard bag sizes and waste.
Calculation Methods
- Rectangular Slabs: Multiply Length × Width × Thickness. (Length and Width in feet, Thickness converted to feet).
- Circular Columns: Use the formula π × (Radius²) × Height.
- The Waste Factor: We recommend adding at least 10% to your calculation to account for spillages, uneven subgrades, or variations in formwork.
Standard Bag Yields
If you are buying pre-mixed bags from a home improvement store, here is what they typically yield:
- 80 lb Bag: Approximately 0.60 cubic feet.
- 60 lb Bag: Approximately 0.45 cubic feet.
- 40 lb Bag: Approximately 0.30 cubic feet.
Example Calculation
If you are pouring a patio that is 10 feet long, 10 feet wide, and 4 inches deep (0.33 feet):
- Volume = 10 x 10 x 0.33 = 33 cubic feet.
- 33 cubic feet / 27 = 1.22 cubic yards.
- Adding 10% waste = 1.34 cubic yards (approx 36.3 cubic feet).
- If using 80lb bags: 36.3 / 0.6 = 61 bags.