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Concrete Footing Calculator — Linear, Pier & Post
Calculate cubic yards and bags for continuous footings, pier footings, and round post holes. Covers foundations, decks, fences, and retaining walls — with depth recommendations by soil type and frost line.
Free Tool
Concrete Footing Calculator
Three footing types in one tool. Select the type that matches your project and enter dimensions — results update instantly.
Results include 10% overage. Costs based on NRMCA 2026 regional averages. Installed costs include excavation and forming. Always consult local building codes for footing depth requirements.
Step by step
How to Calculate Concrete for Footings
Footings are structural — getting the depth and width wrong is a code violation and a safety issue. Here's what matters.
Check your frost line first
IRC R403.1 requires footings to extend below the frost line. In Miami that's 0 inches. In Minneapolis it's 42 inches. Find your local frost depth in the guide below before you dig — the depth determines everything else.
Size width to 2× the wall
IRC R403.1 requires footing width to be at least twice the wall or stem width. A 6-inch concrete wall needs a 12-inch wide footing minimum. Add 2 inches per side if soil is soft or poorly drained.
Choose linear, pier, or round post
Linear footings run continuously under walls and foundations. Pier footings are rectangular blocks under columns. Round post holes use tube forms (Sonotubes) for deck posts, fence posts, and pergolas.
Add rebar before pouring
IRC requires at least two #4 horizontal rebar for continuous footings. Pier and post footings need vertical rebar for uplift resistance in high-wind or seismic zones. Never pour without rebar in structural footings.
IRC R403 + ACI 318
Footing Depth, Width & Frost Line Guide
The two most common footing mistakes: going too shallow (frost heave) and going too narrow (structural failure). This table covers both.
Frost Line Depth by Region — Minimum Footing Depth
| Region / State examples | Frost Depth | Min. footing bottom | Notes |
|---|---|---|---|
| South (FL, TX Gulf, LA, SC coast) | 0–6" | 12" | IRC minimum 12" even in frost-free zones |
| Southeast (GA, AL, MS, AR, TN) | 6–12" | 18" | Occasional freezes require protection |
| Mid-Atlantic (VA, NC, MD, DE) | 12–18" | 24" | Check local amendments |
| Midwest South (KY, MO, KS, OK) | 18–24" | 30" | Variable — consult local code |
| Midwest North (OH, IN, IL, IA) | 24–36" | 42" | Chicago requires 42" minimum |
| Northeast (NY, PA, NJ, CT, MA) | 36–48" | 48" | NYC requires 48" |
| Upper Midwest (MN, WI, MI, ND, SD) | 48–60" | 60" | Minneapolis requires 60" minimum |
| Mountain (CO, UT, WY, MT) | 36–48" | 48" | Elevation varies significantly |
| Pacific Northwest (OR, WA) | 12–24" | 24" | West of Cascades: mild. East: severe. |
| Alaska | 60–100"+ | Engineered | Permafrost — requires structural engineer |
Footing Size by Project Type
| Project | Footing Width | Footing Depth | Rebar | Notes |
|---|---|---|---|---|
| 8" concrete wall | 16" | 8–12" | 2× #4 horiz. | IRC minimum width = 2× wall |
| 6" block wall | 12–16" | 8" | 2× #4 horiz. | Check local code for step-downs |
| Deck (4×4 post) | 10" round | Below frost+6" | #4 vertical | Sonotube form. Belling bottom adds capacity. |
| Deck (6×6 post) | 12–16" round | Below frost+6" | #4 vertical | Min. 18" dia. for heavy loads |
| Fence post (wood) | 3× post width | 1/3 post height + 6" | None | Dry-pack concrete acceptable |
| Retaining wall (<4 ft) | 24" | 24" | 2× #5 horiz. | Drainage behind wall required |
| House foundation | 24" | Below frost line | 2× #5 horiz. | Engineered design required |
Post Hole Quick Reference — Bags per Hole
| Post Size | Hole Diameter | Hole Depth | 80 lb bags / hole | Fast-Set 50 lb / hole |
|---|---|---|---|---|
| 4×4 | 10" | 36" | 2 | 3 |
| 4×4 | 10" | 48" | 3 | 4 |
| 6×6 | 12" | 42" | 3 | 4–5 |
| 6×6 | 14" | 48" | 4 | 6 |
| 8×8 | 16" | 54" | 6 | 8 |
Common Questions
Concrete Footing Calculator FAQ
IRC Section R403.1 requires footings to extend at least 12 inches below undisturbed soil and below the local frost line. In frost-free zones (South Florida, Gulf Coast), 12 inches is the minimum. In Minneapolis, the frost line is 60 inches — footings must go deeper. Check your local building department for the required frost depth in your zip code before digging.
IRC R403.1 requires footing width to be at least twice the supported wall thickness. For a standard 8-inch concrete wall, the minimum footing width is 16 inches. For typical residential construction on stable soil, a 24-inch wide footing provides adequate bearing capacity for most one and two-story structures. On clay or expansive soil, increase width by 25–50%.
A standard 4×4 deck post in a 10-inch diameter hole at 36 inches deep needs about 2 bags of 80 lb concrete per hole. A 6×6 post in a 12-inch hole at 42 inches deep needs about 3 bags. Use the Round Post Hole tab above to calculate any combination of diameter, depth, and number of holes instantly.
Yes — Quikrete Fast-Set and Sakrete Fast-Setting Concrete are code-compliant for post holes and deck footings and reach working strength in 4 hours vs. 24 hours for standard mix. They are not recommended for continuous foundation footings, which require standard 3,000+ PSI ready-mix with proper water-to-cement ratio control. Fast-set is ideal for fence posts, deck posts, and mailboxes.
IRC requires a minimum of two #4 horizontal rebar bars for continuous foundation footings — no exceptions for structural applications. Post hole footings for decks need vertical #4 rebar for uplift resistance in high-wind zones. Fence post holes can use dry-pack concrete without rebar for non-structural applications. Never skip rebar in foundation or structural footings.
Continuous foundation footings cost $15–$30 per linear foot installed in 2026, including excavation, forming, concrete, rebar, and labor. Post hole footings run $20–$60 per hole depending on depth and diameter. Material-only costs (ready-mix concrete) run $120–$165 per cubic yard depending on region — use the calculator above to get your exact material quantity.
Footing depth and width requirements verified against IRC 2021 Section R403, ACI 318-19, and local amendments for 15 major US metro areas. Frost line data from USDA frost depth maps. Post hole bag counts verified against Quikrete and Sakrete published coverage charts. Updated June 2026.