How this calculator works
A footing is a simple box of concrete. We multiply the length by the width and depth, with width and depth converted from inches to feet, then add your waste allowance and convert to cubic yards.
Worked example: a 40 ft continuous footing, 16 in wide and 8 in deep: 40 × 1.333 × 0.667 = 35.6 ft³, or 1.32 yd³ before waste. With 10% waste that is about 1.45 yd³, or 66 bags of 80 lb.
For round pier footings or sonotubes, use the post-hole and column calculator, which handles circular volumes.
Tips before you buy
- Footing width, depth and reinforcement are set by your local code, soil bearing capacity and the load above. Get them from your plans or building department, not from a calculator.
- In cold climates the base of the footing must be below the frost line.
- Digging a footing by hand without forms? Use 10 to 15% waste, since the trench walls are rough.
Tools & materials for this project
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Frequently asked questions
How wide should a concrete footing be?
It depends on the load, the soil and local code. Your building department or engineer decides. Light structures such as sheds and small decks often use footings sized by span tables in the code.
How much concrete do I need for a 12 inch footing?
Per linear foot, a 12 in wide by 8 in deep footing needs 0.67 ft³ (0.025 yd³). Multiply by your total run and add waste, or enter it above.
Do footings need rebar?
Most code-built footings do, especially for house foundations. Requirements vary by location, so follow your plans.
Related calculators & guides
Estimates only. Results assume standard materials and simple shapes. Supplier products vary, and the final call on quantity, structure and safety is yours. Check your local code and your supplier's guidance before ordering.