Concrete Calculator for Deck Footings
Concrete is sold by the bag at the store and by the yard from a truck, and deck footings sit awkwardly between the two. This works out the exact volume for your footing size and count, converts it to both 60 and 80 pound bags with a waste allowance, and tells you the point where ready-mix becomes the cheaper option.
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Frequently asked questions
- How many bags of concrete for a deck footing?
- A 12 inch diameter footing poured 42 inches below grade and 4 inches above holds about 3.0 cubic feet. An 80 pound bag yields 0.60 cubic feet, so that is five bags per footing, or six with a waste allowance. Six footings of that size come to roughly 34 eighty-pound bags — around 2,700 pounds of material.
- How deep should deck footings be?
- Below the local frost line, whatever that is where you live — 12 inches in parts of the south, 42 to 48 inches across much of the north, deeper in the coldest regions. Your building department publishes the figure and will not accept less. A footing that stops above the frost line gets pushed up every time the ground freezes, and the deck racks or pulls away from the house.
- Is it cheaper to use bags or ready-mix for deck footings?
- Bags win under about one and a half cubic yards, which is roughly six to eight standard footings. Past that, the labour of mixing and the cost per cubic foot both turn against you, and a short-load delivery becomes competitive even with the minimum charge and delivery fee. Get a quote — short-load pricing varies a lot by supplier.
- Do deck footings need a flared base?
- It depends on your soil and the load each post carries. A bell-shaped footing form or a poured pad spreads the load over a wider area, which matters in soft or clay soils and under posts carrying a beam or a roof. On firm soil with a modest deck, a straight tube to the correct depth is usually accepted. Your inspector decides.
