Calculate concrete for strip footings (continuous foundation footings) and spread footings (pad footings for columns and posts). Get cubic yards, bag counts, rebar, and cost estimates.
Footing Details
10% recommended for form spillage and over-excavation
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Last updated March 2026 by our expert review team
Ready-mix delivery prices. Add $50-$100 for short-load fees on orders under 3 cubic yards.
Ehsan Ghazanfari
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FISE-certified structural engineer with 11+ years designing bridges, retaining walls, and foundations. MSc from Aalto University.
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AACE-certified estimator working with 20+ insulation companies including the two largest franchises in America.
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How we verify our calculatorsStrip footings (continuous footings) run along the full perimeter of a foundation wall. They spread the wall load across a wider area of soil.
Use our concrete slab calculator for the floor slab that sits inside the foundation footings.
For round pier footings (sonotubes), use our concrete cylinder calculator instead.
Footing width should be at least twice the width of the wall it supports. A 2x6 framed wall on a plate needs a minimum 12-inch wide footing.
Always pour footings on undisturbed native soil. If you over-excavate, fill with compacted gravel, not loose backfill.
Place #4 rebar 3 inches from the bottom of the footing and 3 inches from each side. Use rebar chairs to hold it in position.
Choose strip footing (continuous trench for walls) or spread footing (individual pads for posts/columns). Enter your dimensions and waste factor.
For strip footings: volume = length x width x depth (converted to feet). For spread footings: volume per pad x number of pads. Both include the waste factor.
Get cubic yards, bag counts (60lb and 80lb), rebar estimates, truckloads, and a ready-mix cost range for your project.
Formulas
Strip: Volume = Length (ft) x Width (in/12) x Depth (in/12)
Spread: Volume = (L x W x D per pad) x Number of Pads
Cubic Yards = Cubic Feet / 27
80lb Bags = Cubic Feet / 0.6
How deep should a concrete footing be?
Residential footings are typically 8 to 12 inches deep. The bottom of the footing must sit below the local frost line, which ranges from 12 inches in the South to 48 inches or more in northern states. Check your local building code.
How wide should a footing be?
The IRC requires footings to be at least 12 inches wide for one-story buildings, 15 inches for two-story, and 18 inches for three-story. Wider footings are needed on weak soils.
What is the frost line and why does it matter?
The frost line is the depth at which soil freezes in winter. Footings placed above it will heave upward as frozen soil expands, cracking the foundation. Your local building department publishes the frost depth for your area.
Do footings need rebar?
Yes. The IRC requires at least two continuous #4 rebar bars running the length of strip footings. Spread footings need rebar in both directions. Rebar prevents cracking from soil movement and temperature changes.
What is the difference between a strip footing and a spread footing?
A strip footing is a continuous trench of concrete that runs under walls. A spread footing (pad footing) is an individual square or rectangular pad under a column or post. Both spread the load to the soil below.
What are the IRC requirements for residential footings?
IRC Section R403 requires minimum 12-inch wide footings for 1-story, bearing on undisturbed soil, with 2 continuous #4 rebar, and a minimum 6-inch projection on each side of the wall.
What soil bearing capacity do I need?
Typical residential soil bearing values: rock 4000+ psf, gravel 3000 psf, sand 2000 psf, clay 1500 psf. Your local code or a geotechnical report will give the design value for your site.
When should I use piers instead of strip footings?
Piers work well for decks, porches, and additions where you do not need a continuous foundation wall. Strip footings are required when supporting a continuous wall or when the structure needs a full perimeter foundation.
Standard attached garage footing. 20x20 garage = 80 linear feet of perimeter footing. Order 3 yards to cover waste.
Full house perimeter for a 40x40 two-story home. Ready-mix is the only practical option at this volume. Plan for one truckload.
Six pad footings for a freestanding deck. Bags are practical at this size. Dig below frost line and place on undisturbed soil.
Room addition footing tied into existing foundation. Use rebar dowels drilled and epoxied into the existing footing for a solid connection.
Not going below the frost line
Footings above the frost line will heave and crack your foundation in winter. Check your local code for minimum depth. In northern states it ranges from 36 to 48 inches.
Undersized width for the load
A footing that is too narrow concentrates load and can sink into weak soil. The IRC requires 12" minimum for one-story and 15" for two-story buildings. Get a soil test if you are unsure.
Skipping rebar in the footing
Concrete is strong in compression but weak in tension. Without rebar, footings crack when the soil shifts. Two continuous #4 bars are the minimum for strip footings.
Pouring on disturbed or loose soil
Backfilled or freshly dug soil compresses over time, causing the footing to settle unevenly. Always pour on undisturbed native soil or properly compacted gravel fill.
Forgetting form boards and stakes
Without forms, the trench walls cave into the wet concrete, wasting material and creating an uneven footing. Use 2x lumber staked every 2 to 3 feet for clean edges.
Important Disclaimer
These estimates are for planning purposes only. Actual costs vary by location, material availability, and project complexity. Always get at least 3 local quotes. This calculator does not replace professional advice.