How to use this calculator
- Measure the trench. Length is the run of the footing. Width is typically 16–24 inches for residential footings (twice the wall thickness). Depth must be below the local frost line.
- Enter dimensions. Length and width usually go in feet; depth in inches is convenient because most footings are 8–12 inches deep.
- Add 10% waste. Footing trenches rarely have square edges, so over-dig is common. Order 10% extra and you will not run short.
- Read your result. You get cubic yards (the unit ready-mix delivers in), cubic feet, and the bag count if you decide to mix on site.
Formula
Volume (yd³) = Length × Width × Depth ÷ 27
Worked example
A continuous footing for a 30 ft × 20 ft house with a 16 in × 8 in footing has a perimeter of 100 ft. Volume = 100 × 1.33 × 0.67 = 89 ft³ = 3.3 yd³. Add 10% waste → order 3.7 yd³ of ready-mix.
Common project sizes
Quick reference for the most common concrete footing calculator use cases. Use these as a sanity check on your calculator inputs.
| Project | Dimensions | Result |
|---|---|---|
| Deck pier (12" sonotube × 4 ft deep) | 3.14 ft³ | 0.12 yd³ · 5 bags (80 lb) |
| Fence post (10" hole × 30" deep) | 1.36 ft³ | 0.05 yd³ · 2 bags (80 lb) |
| Shed footing (20 ft perimeter, 8×8 in) | 8.9 ft³ | 0.33 yd³ · 14 bags (80 lb) |
| House perimeter (30×40 ft, 16×8 in) | 124 ft³ | 4.6 yd³ · ready-mix only |
| Retaining wall footing (40 ft × 24×12 in) | 80 ft³ | 2.96 yd³ · ready-mix |
2026 cost reference
Typical retail price range in the United States for concrete footing. Local pricing varies by region, supplier, and grade — confirm with two or three quotes before ordering.
Per cubic yard (delivered ready-mix)
$130 – $180
Footing concrete is usually 3,000 PSI ($130–$155/yd³). Bump to 4,000 PSI ($150–$180/yd³) for retaining walls or expansive soils. Excavation cost varies wildly by access — count $5–$15/linear foot for a backhoe-trenched footing in standard soil. Add $150–$400 for forming materials if you cannot reuse 2× lumber.
How we calculate this
Assumptions baked in
Footing volume = π × (D/2)² × Depth for cylindrical sonotube pours, or L × W × D for rectangular grade-beam footings. Default frost depth is 36 inches (zones 5–6 of the IRC frost-depth map); set it to your local building department's minimum if different. Default sonotube diameter is 12" (typical for deck posts and pergola columns). Bag count uses the same Quikrete yields as the main concrete calculator.
Accuracy and margin of error
Cylinder volume is exact. Bell-bottom footings (wider at the base for bearing) are NOT modeled — for those, calculate the cylinder portion and add the bell separately (treat the bell as a frustum). For ICC-1 helical piles or screw piles, this calculator does not apply; talk to the engineer who specified them.
Edge cases this calculator does not handle
Frost depth in the upper Midwest and New England reaches 48–60 inches — always confirm with your AHJ before ordering. In expansive clay soils (Texas, Colorado Front Range), footings need to extend below the active zone, often 7–10 ft, and require engineering. For coastal salt-exposure zones (Florida, NC outer banks), spec a Type V cement with 4,000+ psi.
Cited sources for this page
The figures and rules above are anchored to the following normative references. We link the underlying claim to its standard — not as generic SEO trust signals, but so you can audit any number on this page against a primary source.
Frost-protected footing depth in IRC Figure R403.1(2) varies from 12" (zone 1, Florida) to 60"+ (zone 8, Northern Maine and Minnesota).
Minimum footing size for residential deck posts (post tributary area × 1,500 psf bearing capacity assumed soil) is published in IRC Table R507.4.
Tips for accurate results
- Footings must extend below the frost line — 12 in in mild climates, up to 48 in in northern states.
- Width is typically 2× the wall thickness above. An 8-inch foundation wall sits on a 16-inch footing.
- For loads under 3 yd³ the short-load fee usually makes bagged pre-mix cheaper.
- Add #4 (½") rebar — typically two continuous bars in the footing, one 3 inches from the bottom.
Common mistakes to avoid
- Pouring above the frost line. The first hard freeze heaves the footing and cracks the wall above. Always confirm the local frost depth before digging.
- Skimping on rebar splices — overlap continuous bars by at least 24 inches and tie them with rebar wire. A non-spliced footing performs like an unreinforced one.
- Backfilling against a green wall. Wait at least 7 days after pouring the wall (and brace it for the first 24 hours) before pushing soil back, or the wall bows.
- Mixing on site for over 1 yd³ — at that point the bagged math says save $50–$80, but the labor and the inevitable cold joints cost more than ordering ready-mix.
When to consult a pro
A footing for a deck or shed (under 1 yd³, no structural load above light framing) is well within DIY range with a tape measure and a level. House perimeter footings, anything supporting a poured wall, and any footing in expansive clay or soft soils should go to a licensed concrete contractor — the cost of a redo (excavation + demolition + permit re-approval) is 5–10× the cost of doing it right the first time. Always pull a permit; an unpermitted footing can void your homeowner insurance.