About this Concrete Calculator
Determining the right amount of concrete is crucial for any masonry project. Buying too little halts your pour mid-job (a disaster), while buying too much wastes money and heavy materials. This calculator determines the volume of your slab or footing and converts it into cubic yards or pre-mix bags.
Who this calculator is for
- DIY homeowners planning slabs, patios, pads, and fence-post footings.
- Contractors estimating ready-mix orders or premix bag counts for smaller pours.
- Anyone converting a measured pour area into cubic yards before ordering.
When to use it
- Estimate cubic yards for a slab, walkway, or shed foundation.
- Convert the same pour into 50 lb, 60 lb, or 80 lb premix bag counts.
- Add a waste factor so the order covers spillage and uneven grade.
How to use this calculator
- Measure the Length and Width of your area in feet.
- Enter the desired Thickness (slab depth) in inches.
- Adjust the Waste percentage (5-10% is recommended for spillage and uneven subgrade).
- Select your Bag Size if using pre-mix concrete.
Key assumptions
- Length and width are in feet, while slab thickness is in inches.
- All dimensions must be positive, and waste cannot be negative.
- Bag counts use a fixed density approximation and should be treated as planning estimates.
Accuracy and testing
Review formula sources, default test cases, assumptions, unit handling, rounding rules, and changelog for this calculator.
How this calculator works
Inputs explained
Dimensions
Enter length and width in feet. Enter thickness in inches (4" is standard for walkways, 6" for driveways).
Waste Factor
Allows for spillage, slight measurement errors, or uneven ground. 5-10% is standard.
Bag Size
Common sizes are 80lb, 60lb, or 50lb bags found at hardware stores.
Understanding your results
Example scenarios
Patio Slab
10x10 ft, 4 inches thick. Volume: 1.23 cubic yards. Bags (80lb): ~56.
Fence Post
1x1 ft footing, 24 inches deep. Volume: 0.06 cubic yards. Bags (80lb): ~3.
Key Features
- Cubic Yard calculation
- Premix bag estimator (80lb, 60lb, 50lb)
- Waste factor included
Tips & Best Practices
- For large projects (> 1 yard), ordering a truck is often easier and cheaper than mixing bags by hand.
- Water content matters. Too much water weakens concrete; too little makes it hard to finish.
- Always wear safety gear (gloves, goggles) as wet concrete is caustic.
Glossary of Terms
- Cubic Yard
- The standard unit for selling bulk concrete (27 cubic feet).
- Screed
- A flat board used to smooth the wet concrete after pouring.
- Cure
- The process of maintaining moisture in concrete so it hardens properly.