Concrete Footing Calculator
Quickly calculate the exact volume of concrete needed for square, rectangular, or circular footings.
1. Enter Footing Dimensions
Select your unit system and footing shape.
2. Get Results
Your results will appear here.
Enter dimensions and press Calculate.
* Price estimations are based on market averages and are for reference purposes only. Please consult local suppliers for accurate quotes.
How to Calculate Concrete for Footings
A strong foundation starts with accurate planning. Concrete footings are critical for distributing the load from posts, columns, or foundation walls to the soil. This calculator helps you find the volume for a single footing. Remember to multiply the result by the total number of footings you need.
How to Determine the Correct Footing Size
Calculating the right size for your footings is just as important as calculating the concrete volume. The size of the footing depends on two main factors: the load of the structure it supports and the load-bearing capacity of the soil.
- Calculate the Total Load: This includes the dead load (the weight of the structure itself) and the live load (potential weight from snow, people, furniture, etc.). For large projects, a structural engineer is recommended.
- Determine Soil Bearing Capacity (SBC): Soil type dramatically affects how much weight it can support. Clay might support 2,000 psf (pounds per square foot), while sandy soil could be higher. You can find general SBC values in local building codes or have a geotechnical engineer test your soil.
- Calculate the Required Area: Divide the total load by the SBC to get the required footing area. For example, a 10,000 lb load on soil with an SBC of 2,000 psf requires a footing area of 5 square feet (10,000 / 2,000).
For common DIY projects, you can often use standard sizes specified by local building codes. Here's a general guide (always verify with your local code):
| Project | Typical Footing Size (Square) | Typical Thickness |
|---|---|---|
| Deck (supporting joists) | 12" x 12" | 8" |
| Small Shed (up to 8'x8') | 16" x 16" | 8" |
| Load-Bearing Post (e.g., for a porch roof) | 24" x 24" | 12" |
| Non-Load-Bearing Wall (Strip Footing) | 16" wide | 8" |
Disclaimer: This table is for informational purposes only. Consult a professional and your local building department before starting any construction project.
Key Considerations for Footing Calculation:
- Frost Line: In cold climates, the bottom of your footing must be below the frost line to prevent heave. This depth varies by region, so check your local building codes.
- Soil Bearing Capacity: The size of your footing (width and length) depends on the load it must support and your soil's ability to bear that load. If you're unsure, consult a structural engineer.
- Shape Consistency: Ensure your footing holes are dug with straight sides and a flat bottom to match the calculated volume. Irregular shapes will require more concrete.
Frequently Asked Questions (FAQ)
What is a footing and why do I need one?
A footing is a concrete base that supports a structure's foundation. It spreads the weight of the structure over a wider area, providing stability and preventing the foundation from settling or shifting. They are essential for almost all permanent structures, from decks to houses.
What is the difference between a footing and a foundation?
Think of it as a sequence: the footing is the wide base at the very bottom that sits on the soil. The foundation (often a wall or piers) is built on top of the footing and directly supports the structure. A footing provides the stable platform the foundation needs.
Should I use a circular or square footing?
Both are common. Square footings are often easier to form with lumber. Circular footings, often made using cardboard form tubes (like Sonotubes), can be easier to dig with an auger. The choice often depends on your construction method and local practices. This calculator handles both rectangular (for strip/pad footings) and circular (for pier) shapes.
To learn more about the fundamental principles of concrete calculation for any shape, visit our comprehensive guide.