Cubic Feet: ft³
Number of 60lb Bags:
How to Use the Concrete Calculator
Ordering the correct amount of concrete is essential for any construction project, whether you are pouring a new backyard patio, a driveway, or footings for a fence. This concrete calculator helps you estimate the total volume of concrete needed in cubic yards and cubic feet, while also providing the number of pre-mixed bags required if you are doing the work yourself.
To get started, follow these simple steps:
- Select Project Shape
- Choose "Rectangular Slab" for squares, rectangles, or walls. Choose "Circular Column" for round post holes or cylindrical pillars.
- Enter Dimensions
- Input the length, width, and thickness. Note that for slabs, thickness is usually measured in inches, while for columns, depth is measured in feet.
- Waste Allowance
- Concrete projects often involve some loss due to spills, uneven subgrades, or variations in formwork. A standard waste factor is 5% to 10%.
How It Works: The Formulas
The math behind a concrete calculator depends on the geometry of the pour. Concrete is typically sold by the cubic yard, which is equal to 27 cubic feet.
Rectangular Slab Formula
Volume (ft³) = Length (ft) × Width (ft) × [Thickness (in) / 12]
To convert the result to cubic yards, divide the total cubic feet by 27.
Circular Column Formula
Volume (ft³) = π × Radius² × Depth (ft)
- π (Pi): Approximately 3.14159
- Radius: Half of the diameter of the hole
- Depth: The vertical height of the column
Calculation Example
Example: Imagine you are pouring a concrete patio that is 12 feet long, 10 feet wide, and 4 inches thick. You want to include a 10% waste factor.
Step-by-step solution:
- Convert thickness to feet: 4 inches / 12 = 0.333 feet.
- Calculate base volume: 12 ft × 10 ft × 0.333 ft = 40 cubic feet.
- Add 10% waste: 40 × 1.10 = 44 cubic feet.
- Convert to yards: 44 / 27 = 1.63 cubic yards.
- Bags (80lb): 44 / 0.60 = 74 bags.
Common Concrete Questions
How many 80lb bags are in a cubic yard?
It takes approximately 45 bags of 80lb pre-mixed concrete to fill one cubic yard. For 60lb bags, you will need approximately 60 bags.
How thick should a concrete driveway be?
For standard passenger vehicles, a thickness of 4 inches is standard. If you expect heavy-duty trucks or equipment to use the driveway regularly, 5 to 6 inches is recommended for increased load-bearing capacity.
What is a standard waste factor?
Most professionals use a 10% waste factor. This accounts for variations in the ground depth (the ground is rarely perfectly flat) and material left inside the mixer or pump.