Concrete Footing Calculator (2026) – Strip, Pad & Post Hole
Calculate concrete for strip footings, pad footings, and round post holes. Get cubic yards, bag counts, and material cost — with frost depth guidance by US region.
For continuous foundation footings, retaining wall footings, and building perimeter footings.
Perimeter of building or total linear footage
Typical: 1.0–2.0 ft wide
Must be below frost line — see guide below
For isolated column footings, post bases, and deck piers (square or rectangular).
For fence posts, deck posts, mailbox posts, and any round concrete-filled hole.
4×4 post: 8–10 in · 6×6 post: 12 in
Minimum 1/3 of post length above grade
Footing Results
Adjust inputs and click Calculate
—
Cubic Yards (with waste)
—Cubic Feet
—Est. Material Cost
—60 lb Bags Needed
—80 lb Bags Needed
Per-Unit Breakdown
Net volume per unit—
Number of units—
Total net volume—
+ Waste—
→ Order this amount—
*Always verify footing depth meets your local frost line requirement before pouring.
Footing Types — Which Do You Need?
| Type | Shape | Used For | Typical Size |
|---|---|---|---|
| Strip / Continuous | Long rectangle | Foundation perimeter, load-bearing walls, retaining walls | 12–24 in wide × 8–18 in deep |
| Pad / Isolated | Square or rectangle | Column bases, deck piers, post bases | 18–36 in square × 12–24 in deep |
| Round (Post Hole) | Cylinder | Fence posts, deck posts, mailbox, signs | 6–12 in diameter × 18–36 in deep |
| Mat / Raft | Large slab | Entire building on poor soil | Engineered — requires structural PE |
Frost Depth Guide by US Region
Footings must be placed below the local frost line — otherwise freeze-thaw cycles will heave the footing, cracking walls and structures above. Always verify with your local building department.
| Region / State | Frost Depth | Notes |
|---|---|---|
| Florida, Southern TX, Southern CA | 0 inches | No frost depth concern |
| Mid-Atlantic (VA, NC, TN) | 8–12 inches | Light frost risk |
| Pacific Northwest (OR, WA) | 12–18 inches | Mild winters — varies by elevation |
| Ohio Valley, Kansas, Missouri | 18–24 inches | Moderate frost |
| New England, Great Lakes (MI, WI) | 36–48 inches | Deep frost — verify locally |
| Minnesota, North Dakota | 42–60 inches | Some of deepest frost depths in US |
| Mountain West (CO, high elevation) | 24–48 inches | Varies by altitude |
Concrete Post Hole Guide
Fence and deck post holes are the most common use of bagged concrete for DIY projects. Here's how much you need for standard configurations:
| Post Size | Hole Dia. | Depth | ft³ per hole | Bags needed |
|---|---|---|---|---|
| 4×4 wood / 2" steel | 8 in | 24 in | 0.70 ft³ | 2 × 40 lb bags |
| 4×4 wood (standard) | 10 in | 24 in | 1.09 ft³ | 2 × 60 lb bags |
| 6×6 wood / 4" steel | 12 in | 30 in | 1.96 ft³ | 3–4 × 60 lb bags |
| Mailbox / sign post | 6 in | 18 in | 0.29 ft³ | 1 × 40 lb bag |
💡 Quikrete Fast-Setting Concrete tip: For fence posts, you can pour the dry mix directly into the hole and add water on top — no mixing required. This method sets in 20–40 minutes, allowing you to continue with the next post. Standard concrete still works fine but requires mixing first.
Footing FAQ
How deep should a concrete footing be?
Footings must be below the local frost line to prevent heaving. In the South, 8–12 inches may be sufficient. In the Midwest and Great Lakes, 36–48 inches is standard. In Minnesota and North Dakota, frost depths can reach 60 inches. Always check with your local building department — they will have the code-required frost depth for your specific zip code.
How many bags of concrete for a fence post hole?
For a standard 4×4 fence post with a 10-inch diameter × 24-inch deep hole: you need approximately 1.09 ft³ of concrete. Use 2 × 60 lb bags (0.45 ft³ each = 0.90 ft³, slightly under) or 2 × 80 lb bags (1.20 ft³ total) for a comfortable margin. The Post Holes mode in this calculator gives exact quantities for any hole diameter, depth, and number of posts.
What is the minimum footing size for a residential structure?
Per the IRC (International Residential Code), minimum continuous footing width for a 1-story structure is 12 inches wide × 6 inches thick; for a 2-story structure, 15 inches wide × 7 inches thick; for a 3-story structure, 23 inches wide × 8 inches thick. These are minimums — your structural engineer or local code may require larger sizes based on soil bearing capacity. Always get a permit for structural footings.
How long does concrete footing take to cure before building on it?
Wait at least 3–7 days before placing any load on a footing. Full design strength (100%) is reached at 28 days. For structural footings under walls or columns, most engineers require a minimum 7-day cure before loading. In cold weather (below 50°F), cure times extend significantly — use insulated curing blankets and avoid pouring when temperatures drop below 40°F.