Concrete Calculator
Calculate the volume of concrete needed for slabs, cylinders, or curbs. Computes cubic yards, cubic feet, and standard bag counts (80lb, 60lb) with customizable waste allowance.
Calculation Results
The total volume of concrete required, including waste.
Number of standard 80lb bags (approx. 0.6 cu ft of mixed concrete per bag).
Number of standard 60lb bags (approx. 0.45 cu ft of mixed concrete per bag).
Total weight of concrete when wet (approx. 150 lbs/cu ft).
How This Calculator Works
To use the concrete calculator, follow these steps:
- Select the shape of your concrete pour (Slab, Column, or Curb).
- Enter the dimensions of your project (e.g. length, width, and thickness). You can select your preferred units (inches, feet, yards, centimeters, or meters) for each input independently.
- Adjust the waste percentage (typically 10% is recommended to account for spillage, uneven ground, and minor errors).
- Review your results: the calculator displays total yards, cubic feet, the count of 80lb/60lb bags, and the total weight of materials.
Formula & Calculations
Concrete volume is calculated by multiplying the surface area of the shape by its thickness or height. Standard formulas are used for each shape:
- Rectangular Slabs:
Length × Width × Thickness - Columns / Cylinders:
π × (Diameter / 2)² × Height - Curbs:
Length × Width × Height
The resulting volume is originally calculated in cubic feet, and then converted to cubic yards by dividing by 27 (since 1 cubic yard = 27 cubic feet).
Concrete bag yields are estimated based on standard weights:
- An 80-pound bag yields 0.60 cubic feet.
- A 60-pound bag yields 0.45 cubic feet.
Step-by-Step Calculation Examples
Standard Patio Slab (10ft x 12ft x 4in)
Calculating concrete volume for a rectangular back patio with a standard 4-inch depth and a 10% waste margin.
- shape: slab
- length: 12
- width: 10
- thickness: 4
- waste: 10
- volume: 1.63 cu yd
- bags_80lb: 74
- total_weight: 3.30 tons
Structural Column (12in Diameter x 8ft Height)
Calculating volume for a concrete support pier column with a 10% waste margin.
- shape: column
- diameter: 12
- height: 8
- waste: 10
- volume: 0.26 cu yd
- bags_80lb: 12
- total_weight: 0.52 tons
Frequently Asked Questions
How much concrete is in a cubic yard?
A cubic yard of concrete is a volume that measures 3 feet by 3 feet by 3 feet, equaling 27 cubic feet. It is enough to cover a 10-foot by 10-foot area at 3 inches deep.
Why should I add a waste factor to my concrete estimate?
Uneven subgrades, shifting forms, spillage during pouring, and consolidation can cause you to run short if you order the exact math volume. A waste factor of 5% to 10% guarantees you have enough to complete the job.
How many bags of concrete make a cubic yard?
It takes forty-five 80lb bags, or sixty 60lb bags of concrete mix to equal one cubic yard (27 cubic feet) of concrete.