Concrete Footing Calculator

Concrete footings must extend below the frost line to prevent heaving. Frost line depth varies by location: 12–18 inches in the southern US, 24–36 inches in the mid-Atlantic and Midwest, and 42–48+ inches in northern states. Check your local building code for the exact frost line depth in your area. Most residential footings are 12–48 inches deep.

A general rule is that footings should be twice as wide as the wall they support. For a standard 8-inch foundation wall, use a 16-inch wide footing. For load-bearing columns, spread footings are typically 24–36 inches square. Pier footings for decks are commonly 12–18 inches in diameter. Always consult local building codes for specific requirements based on soil bearing capacity and loads.

A standard deck pier footing (12” diameter × 36” deep) uses about 2.4 cubic feet or 0.09 cubic yards of concrete. For 4 deck piers, you'll need approximately 0.35 cubic yards (about 16 bags of 80 lb concrete). For larger 18” diameter piers, each uses about 5.3 cubic feet — roughly doubling the concrete needed.

Yes, rebar is recommended for most concrete footings. For pier footings, use 2 pieces of #4 rebar placed vertically. For continuous wall footings, run 2 continuous #4 rebar horizontally, with pieces placed every 4 feet along the length. For spread footings, use a grid of #4 rebar (typically 4 pieces per footing). Rebar prevents cracking and provides tensile strength that concrete alone lacks.

A pier (or cylindrical) footing is a round column of concrete, typically used for deck posts, porch supports, and light structures. A spread (or pad) footing is a rectangular block of concrete that distributes a column load over a wider area, used for heavier structural columns and posts. Continuous (strip) footings run the length of a wall and support the entire wall structure.

It depends on the footing size. An 80 lb bag of concrete yields 0.022 cubic yards (about 0.6 cubic feet). A single 12” diameter × 36” deep pier footing needs about 4 bags of 80 lb concrete. A 20 ft continuous wall footing (12” wide × 8” deep) needs about 30 bags. Use our calculator above for exact quantities based on your specific dimensions.

Concrete should not be poured when temperatures are below 40°F (4°C) or when freezing temperatures are expected within 24 hours. Cold weather slows curing and can cause the concrete to freeze before gaining strength, resulting in weak, crumbly footings. If you must pour in cold weather, use hot water in the mix, insulated blankets, and consider accelerating admixtures. Never pour directly on frozen ground.

Concrete footings should cure for at least 7 days before applying any structural load, and 28 days for full strength. During curing, keep the concrete moist by covering with plastic sheeting or applying curing compound. In warm weather (above 70°F), concrete reaches about 70% of its strength within 7 days. In cooler weather, allow additional curing time before building on the footings.