Concrete Footing Calculator
Calculate how much concrete you need for deck footings, pier foundations, and continuous footings.
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How to Calculate Concrete for Footings
Concrete footings are the foundation of any structure — decks, additions, fences, and retaining walls all start here. To calculate the concrete needed, multiply the footing's length (in feet) by width and depth (converted from inches to feet). Multiply by the number of footings, then add your waste factor.
The formula is: Volume per footing (ft³) = Length × (Width ÷ 12) × (Depth ÷ 12). Multiply by the number of footings for total volume, then divide by 27 for cubic yards.
Tips for Concrete Footings
- Dig below the frost line.Footings that don't extend below the frost line will heave and shift with freeze-thaw cycles, causing structural damage above.
- Use flat-bottomed holes. A footing needs a flat, level base to distribute load evenly. Round-bottomed post holes concentrate force at one point.
- Keep footings level. Use a laser level or string line across the tops of your forms to ensure all footings are at the same elevation.
- Place anchor bolts or post brackets while wet. J-bolts and post bases must be set into wet concrete. Have them ready and positioned before you pour.
Types of Footings
Spread footingsare flat, wide pads that distribute the load of a post or column over a larger area. They're the most common type for decks and sheds.
Continuous footings(strip footings) run the length of a wall and are used for foundations, retaining walls, and load-bearing walls. They're wider than the wall they support.
Pier footings are cylindrical, often poured using Sonotube forms. Use our concrete column calculator for round pier footings.
Frequently Asked Questions
- How deep should concrete footings be?
- Footings must extend below the frost line in your area — typically 12 inches in mild climates, 36–48 inches in northern states. Check your local building code for the exact frost depth requirement. In most cases, 12 inches of depth is the minimum for structural footings.
- How wide should a footing be?
- A footing should be at least twice as wide as the wall or post it supports. For a standard deck post on a 6×6 post, a 12-inch wide footing is typical. Foundation wall footings are usually 16–24 inches wide depending on the load.
- Do I need rebar in my footings?
- For structural footings supporting a deck, addition, or retaining wall — yes. Continuous footings should have at least two #4 rebar running lengthwise, and shorter footings benefit from rebar to prevent cracking. Check local codes for specific requirements.
- How long does a concrete footing need to cure?
- Concrete reaches about 70% strength in 7 days and full strength in 28 days. You can typically begin building on footings after 3–7 days in warm weather, but avoid placing heavy loads for at least a week.