Concrete Calculator
Calculate exactly how much concrete volume and pre-mixed bags you need for your next slab, footing, or stairs project.
* Bag estimates include a standard +10% waste margin recommended for all concrete pours.
Concrete Volumes by Shape
The Premise: Buying the wrong amount of concrete can ruin a project. Too little creates a cold joint, while too much wastes money.
The Evidence: The exact mathematical formulas are Length × Width × Depth for a slab. However, this is converted into cubic yards since that is the industry standard unit.
The Conclusion: Utilizing our Concrete Calculator ensures you order exactly the right amount of concrete for any geometric shape, avoiding waste and ensuring structural integrity.
How to Use the Calculator
- Select the shape of your pour: Slab, Column, or Stairs.
- Enter the exact dimensions of your project (Length, Width, and Depth) in your preferred units.
- Click the "Calculate Volume" button.
- Review the cubic yards required, along with the bag count for 40lb, 60lb, and 80lb bags.
Limitations
Please note the following limitations: This calculator assumes a perfect geometric shape. Real-world conditions like uneven subgrades or bowed forms will alter the required volume. Always include at least a 10% waste factor (which this tool calculates automatically).
Data Privacy & Security
Your privacy is important to us. All calculations performed by the Concrete Calculator happen locally within your web browser. We do not store, track, or transmit your project dimensions to any server.
Frequently Asked Questions
Why do I need to add 10% extra?
It is an industry standard to order 10% more concrete than your exact mathematical volume. Forms can bow, the subgrade might be uneven or slightly deeper in spots, and some concrete always spills or remains in the mixer. Running out of concrete mid-pour is a disaster.
Should I use 60lb or 80lb bags?
80lb bags are more economical and mean less mixing, but they are very heavy and can cause back strain if you are mixing a lot of them by hand. 60lb bags are much easier to handle for a single person doing a DIY project.
When should I order a concrete truck instead of bags?
As a general rule of thumb, if your project requires more than 1 cubic yard (about 45 of the 80lb bags), it is highly recommended to order a ready-mix truck. Mixing that many bags by hand or even with a small portable mixer is incredibly labor-intensive.
How do I calculate concrete for a slab?
Multiply length x width x depth (all in feet), then divide by 27 to get cubic yards.
How many bags of concrete make a yard?
It takes forty-five 80lb bags, sixty 60lb bags, or ninety 40lb bags to equal one cubic yard of concrete.
Is the concrete calculator free?
Yes, our concrete calculator is 100% free to use.
Can I use this on mobile?
Yes, this tool is fully responsive and works directly in your mobile browser without installing an app.
Does this tool collect my data?
No, all calculations are performed locally in your browser. No data is sent to our servers.
What if my pour is a custom shape?
For complex custom shapes, it is best to break the area down into smaller rectangles or cylinders, calculate the volume for each separately, and then add the cubic yards together.