Concrete Footing & Foundation 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. Unsure about dimensions? See our sizing guide below.
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 Determine Your Footing Size
Before you can calculate volume, you need the right dimensions. The size of your footing depends on the building load and your soil's strength.
1. Calculate Total Load
Determine the total weight the footing must support. This includes the structure's own weight (dead load) and potential weight from snow, people, etc. (live load). For anything beyond a simple deck or shed, consulting a structural engineer is recommended.
2. Find Your Soil's Bearing Capacity (SBC)
Different soil types support different weights. Check your local building codes for the SBC in your area. It's typically measured in pounds per square foot (psf). (e.g., Clay: ~1,500 psf, Sand/Gravel: ~3,000 psf).
3. Calculate Required Footing Area
Required Area (sq. ft.) = Total Load (lbs) / Soil Bearing Capacity (psf)
For example, a 12,000 lb load on soil with a 2,000 psf capacity requires a footing area of 6 sq. ft. (12,000 / 2,000). This could be a 2 ft x 3 ft footing.
Understanding 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.
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.