Concrete slab estimates
Estimate ready-mix volume for patios, walkways, shed pads, and other rectangular slabs.
Concrete Calculator
Estimate concrete volume for a rectangular or circular slab, add a waste allowance, and compare cubic yards with approximate 40, 60, or 80 lb bag counts.
Material Calculator
Advanced material settings
Current settings: 10% waste · 80 lb bag yield available in Advanced settings.
Enter the project dimensions to see the material estimate
The estimate includes the selected waste allowance. Confirm order minimums, truck capacity, and bag yield with the supplier.
What Is Concrete Calculator?
A concrete calculator estimates the wet concrete volume needed for a slab or circular pad. It reports cubic feet, cubic yards, and cubic meters, which can help compare a ready-mix order with packaged concrete.
The bag calculation divides adjusted volume by an approximate yield for the selected 40, 60, or 80 lb bag. Bag yield varies by product, so the manufacturer's label should replace the default assumption when precision matters.
How to Use Concrete Calculator
1
Choose the Concrete Shape
Select Rectangle for a slab or Circle for a round pad, then enter dimensions in feet.
2
Enter Slab Thickness
Enter the planned concrete thickness in inches using the project design.
3
Set Waste and Bag Size
Adjust the waste allowance and choose the bag size when comparing packaged concrete.
4
Review the Live Concrete Quantity
Cubic yards, cubic meters, bag count, and optional ready-mix cost update automatically.
How the Concrete Calculator Works
The calculator multiplies slab area by thickness, converts inches to feet, and increases the result by the selected waste allowance.
Cubic yards equal adjusted cubic feet divided by 27. The bag estimate divides adjusted cubic feet by the selected approximate bag yield and rounds up to a whole bag.
Concrete yd³ = Area (ft²) × Thickness (in ÷ 12) × (1 + Waste %) ÷ 27
Example
A 12 ft by 10 ft slab at 4 inches thick has 40 ft³ of raw volume. With 10% waste, it requires 44 ft³ or 1.63 yd³, equal to about 74 bags when an 80 lb bag yields 0.60 ft³.
Concrete Calculator Features
- Calculates rectangular slabs and circular pads
- Reports cubic feet, cubic yards, and cubic meters
- Includes an adjustable waste allowance
- Estimates 40, 60, or 80 lb bag quantities
- Calculates optional ready-mix material cost per cubic yard
Common Use Cases
Circular pad planning
Calculate volume for a round equipment base or other simple circular placement.
Ready mix versus bags
Compare the cubic-yard estimate with an approximate bag count before considering labor and delivery constraints.
Limits and Important Notes
- Bag yields are approximate; use the yield printed on the selected product for purchasing.
- Footings, thickened edges, grade beams, slopes, voids, and irregular excavation require separate measurements or a more detailed takeoff.
- The estimate does not design slab thickness, reinforcement, concrete strength, joints, subbase, or structural capacity.
- Ready-mix suppliers may impose minimum orders, short-load fees, truck limits, and order increments.
Related Tools
Material Calculator
Choose a construction material calculator to estimate how much material your project needs from its measured area, depth, and waste allowance.
Gravel Calculator
Estimate gravel volume and weight for a driveway, path, drainage layer, or landscape area using measured dimensions and an editable density.
Sand Calculator
Estimate how much sand a rectangular or circular area needs from its dimensions, fill depth, waste allowance, and expected bulk density.
Asphalt Calculator
Estimate asphalt tons for a rectangular or circular paving area using its dimensions, compacted thickness, waste allowance, and material density.