How deep should concrete footings be?

Concrete footings must extend below the frost line to prevent frost heave. Frost depth varies by region — from 12 inches in the South to 48+ inches in the northern US. Always check local building codes. Footings are typically a minimum of 12 inches deep regardless of frost depth.

How wide should concrete footings be?

Residential wall footings are typically twice as wide as the wall they support — a standard 8-inch wall needs a 16-inch wide footing. Column footings for decks or porches are typically 12–24 inches square depending on load.

How many bags of concrete for a footer?

Calculate the volume of your footing (length × width × depth, all in feet), then divide by 27 for cubic yards. Each 60 lb bag covers 0.45 cubic feet, so: bags needed = (cubic feet) ÷ 0.45.

Does a concrete footing need rebar?

Most building codes require at least two runs of #4 rebar in residential footings, placed in the lower third of the footing. Check your local code — some jurisdictions require engineered footing plans for certain structures.

What PSI concrete should I use for footings?

Residential footings typically require 3,000 PSI concrete at minimum. For areas with freezing temperatures or high soil moisture, use 3,500–4,000 PSI with a low water-to-cement ratio. Footings exposed to sulfate soils may require Type V cement or a higher PSI mix per the soils report.

How soon can you build on a new concrete footing?

You should wait at least 7 days before placing any significant load on a new footing — at that point the concrete has reached approximately 70% of its 28-day design strength. For critical structural applications (multi-story walls, heavy columns), wait the full 28 days. Never build on a footing that has been poured fewer than 3 days ago, even for light framing. Protect the footing from traffic and keep it moist for the first 7 days to ensure proper curing and full strength development.

What is the difference between a footing and a foundation?

A footing is the widened, lowest element of a structure that distributes the load into the soil. A foundation encompasses all the below-grade structural elements, including the footings, stem walls, and grade beams. The footing bears directly on undisturbed soil or rock; everything above it is the foundation. Residential footings are typically 8–16 inches thick and are sized so the bearing pressure on the soil (load ÷ footing area) stays within the safe bearing capacity of the soil — typically 1,500–3,000 lbs per square foot for undisturbed native soil.

Concrete Footing Calculator — Volume, Bags, Weight & Cost

Estimates volume, bags needed, weight, and cost for concrete footings and foundation footers.

What Is a Concrete Footing?

This concrete footing calculator helps size the base element of any foundation system — a widened, low-profile concrete pad or strip that spreads structural loads across a large enough soil area to stay within the soil's safe bearing capacity. Footings must be placed on undisturbed soil (never on fill) and must extend below the frost line to prevent frost heave from lifting the structure each winter.

IRC R403.1 sets minimum residential footing dimensions: width must be at least twice the wall thickness, and depth must be at least 12 inches below grade and below the local frost line. Residential footings typically require 3,000 PSI concrete with two horizontal #4 rebar placed in the lower third. Frost depths range from 12 inches in the deep South to 48+ inches in the northern US — always confirm the local requirement with your building department before digging.

How to Use This Concrete Footing Calculator

This concrete footing calculator estimates volume, bags, weight, and cost for any footing shape. Choose your shape — rectangular strip, round pier, square pad, Bigfoot bell form, or enter a known area — then input the dimensions and quantity. Use it for house foundations, deck piers, column pads, retaining wall footers, and any other footing project. For a combined slab-and-footing estimate, try our slab and footing calculator.

How to Calculate Concrete for Footings

The formula depends on the footing shape:

Rectangular / Strip Footing

Volume = Length × Width × Depth ÷ 27 (all dimensions in feet, result in cubic yards). A 40-foot footing that is 16 inches wide and 12 inches deep: (40 × 1.333 × 1.0) ÷ 27 = 1.97 cubic yards. With 10% waste, order 2.2 cubic yards.

Round Pier Footing

Volume = pi × (Diameter / 2)² × Depth. Five 12-inch diameter piers at 36 inches deep: each = 2.36 ft³, total = 11.78 ft³ = 0.44 cubic yards.

Square Pad Footing

Five 18×18 inch square pads each 12 inches deep: (1.5 × 1.5 × 1.0) × 5 ÷ 27 = 0.42 cubic yards total. This is manageable with bags — about 25 bags (60 lb).

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Footing Size Requirements

The size of a footing depends on the load it must carry and the bearing capacity of the soil beneath it. General residential guidelines:

8-inch foundation wall — footing 16 inches wide × 8 inches deep (minimum)
10-inch foundation wall — footing 20 inches wide × 10 inches deep
Deck post (4×4) — 12-inch square pad, depth to frost line
Deck post (6×6) — 16–18 inch square pad, depth to frost line
Frost depth — varies from 12 inches in the deep South to 48+ inches in northern states; check with your local building department

Footing Construction Tips

Dig below the frost line — footings that don't go deep enough will heave in winter, damaging the structure above; always check local frost depth requirements
Bear on undisturbed soil — never place footings on disturbed or filled soil without engineering; compacted soil or gravel is required for a stable base
Rebar is required — most codes require at least two runs of #4 rebar in the bottom third of the footing; tie vertical dowels for wall-to-footing connections
Wet the excavation — lightly dampen the soil before pouring to prevent the dry earth from pulling water out of the fresh concrete too quickly
Protect the cure — cover footings with plastic sheeting for at least 7 days to retain moisture and allow full strength development before building on them
Plan the full slab — if your footing supports a floor, use our concrete slab calculator to estimate the slab volume separately and order both pours together

Sources & References

IRC Section R403: Footings — International Residential Code — International Code Council
ACI 318-19: Building Code Requirements for Structural Concrete — American Concrete Institute
ASTM C94/C94M: Standard Specification for Ready-Mixed Concrete — ASTM International

How Much Does a Concrete Footing Cost?

Concrete footing costs depend on the footing type, size, and whether you hire a contractor or DIY. For materials alone, ready-mix concrete runs $130–$165 per cubic yard delivered, while 80 lb bags of Quikrete cost about $5.50–$7.00 each (roughly $185–$235 per cubic yard when buying bags). A typical residential strip footing for a 40-foot wall — roughly 2.2 cubic yards with waste — costs $285–$365 in concrete alone. Five round pier footings for a deck average $35–$55 in bagged concrete.

Labor is the biggest cost multiplier. Professional footing installation runs $6–$12 per linear foot for strip footings and $75–$200 per pier for round footings, including excavation, forming, rebar, and concrete. A 120-linear-foot perimeter footing for a small addition typically costs $1,500–$3,500 fully installed. Add $150–$400 for a building permit and inspection in most jurisdictions. Use our concrete cost calculator to get a detailed material cost breakdown for your specific project.