How long does a 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. In cold weather below 50°F, cure times extend significantly.

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Concrete Footing Calculator (2026) – Strip, Pad & Post Hole

Q: How deep should a concrete footing be?

Footings must be placed below the local frost line. 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 for the code-required frost depth.

Q: What is the minimum footing size for a residential structure?

Per the IRC, minimum continuous footing width for a 1-story structure is 12 inches wide × 6 inches thick; 2-story: 15 inches wide × 7 inches thick; 3-story: 23 inches wide × 8 inches thick. These are minimums — local code or soil conditions may require larger sizes.

Q: What is the difference between a footing and a foundation?

A footing is the widened base that distributes the load of a wall or column into the soil. The foundation is the vertical element (wall or piers) that sits on top of the footing. Footings must be wider than the structure above to spread load over a larger soil area.

Q: How wide does a concrete footing need to be?

A common rule of thumb is that footing width should be at least twice the width of the wall it supports. For a standard 8-inch concrete block wall, the footing should be at least 16 inches wide. Most residential strip footings range from 12–24 inches wide depending on load and soil bearing capacity.

Q: Do I need rebar in a concrete footing?

Yes, for most structural footings. Horizontal rebar placed near the bottom of a strip footing adds tensile strength to resist bending from soil pressure. Most building codes require a minimum of two #4 horizontal bars in continuous footings. Post hole footings for fences generally do not require rebar.

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.

Total Length (ft)

Perimeter of building or total linear footage

Width (ft)

Typical: 1.0–2.0 ft wide

Depth (ft)

Must be below frost line — see guide below

For isolated column footings, post bases, and deck piers (square or rectangular).

Length (ft)

Width (ft)

Depth (ft)

Quantity

For fence posts, deck posts, mailbox posts, and any round concrete-filled hole.

Hole Diameter (in)

4×4 post: 8–10 in · 6×6 post: 12 in

Hole Depth (in)

Minimum 1/3 of post length above grade

Number of Holes

Price ($/yd³)

Waste (%)

Footing Results

Live calculation active

0.00 yd³ 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.

What is the difference between a footing and a foundation?

A footing is the widened base that distributes the structural load into the soil. It's typically wider than the wall or column above it to spread load over a larger bearing area. The foundation refers to the vertical element — wall, piers, or grade beam — that sits on top of the footing and transfers building loads down to it. Think of the footing as the foot and the foundation as the leg. Both must be designed together based on soil bearing capacity and structural loads.

How wide does a concrete footing need to be?

A widely used rule of thumb is that footing width should be at least twice the width of the wall it supports. For a standard 8-inch concrete block wall, the footing should be at least 16 inches wide. For an 8-inch poured concrete wall, a 16-inch wide footing is the IRC minimum for a one-story structure. Wider footings are required on soft or expansive soils where the bearing capacity is lower than average.

Can I pour a footing in cold weather?

Concrete should not be poured when ambient temperatures are below 40°F without cold-weather precautions. Options include: insulated curing blankets, heated enclosures, hot water in the mix, or accelerating admixtures. Fresh concrete that freezes before achieving at least 500 PSI will lose up to 50% of its final design strength — damage that cannot be reversed. Many contractors refuse to pour footings when a freeze is forecast within 24 hours of the pour.

Do I need rebar in a concrete footing?

Yes, for most structural footings. Horizontal rebar near the bottom of a strip footing adds tensile strength to resist bending from uneven soil pressure and differential settlement. Most building codes require a minimum of two #4 (½-inch) horizontal bars in continuous footings, placed 3 inches from the bottom. Vertical dowels are required where the footing connects to a poured concrete wall above. Post hole footings for fences and mailboxes do not require rebar unless specified by local code.

Worked Examples: Footing Concrete Calculations

Example 1 — Strip Footing for a Garage

A detached 2-car garage (20×24 ft) needs a continuous perimeter footing. The footing is 16 inches wide × 10 inches deep.

Perimeter: (20 + 24) × 2 = 88 linear feet
Width in feet: 16 / 12 = 1.333 ft
Depth in feet: 10 / 12 = 0.833 ft
Volume (net): 88 × 1.333 × 0.833 = 97.8 ft³ = 3.62 yd³
With 10% waste: 3.98 yd³ — order 4.0 yd³
Bags alternative: 3.98 yd³ × 45 bags/yd³ = 179 × 80 lb bags

At $160/yd³, material cost is ~$638. At $10.50/bag, bags would cost ~$1,880 — nearly 3× more. Ready-mix is clearly the right choice here.

Example 2 — Pad Footings for a Deck (6 posts)

A deck is supported by 6 posts, each on a 24×24-inch pad footing, 12 inches deep.

Volume per pad: 2.0 × 2.0 × 1.0 = 4.0 ft³
Total for 6 pads: 4.0 × 6 = 24.0 ft³ = 0.89 yd³
With 10% waste: 0.98 yd³
80 lb bags: ⌈26.4 / 0.60⌉ = 44 bags
Bag cost: 44 × $10.50 = ~$462
Ready-mix: 0.98 yd³ × $160 + $140 short-load fee = ~$297

Even with the short-load fee, ready-mix is cheaper for this volume — but bags are more convenient if truck access to the deck location is difficult.

Example 3 — Fence Post Holes (20 posts)

A 100-foot privacy fence uses 20 posts (5-foot spacing), with 10-inch holes, 30 inches deep.

Volume per hole: π × (5/12)² × (30/12) = 3.1416 × 0.1736 × 2.5 = 1.36 ft³
Total: 1.36 × 20 = 27.2 ft³
With 10% waste: 29.9 ft³ = 1.11 yd³
80 lb bags: ⌈29.9 / 0.60⌉ = 50 bags

At ~$10.50/bag, total bag cost is ~$525. Most DIYers use bags for fence posts because the work is spread over multiple days and Quikrete Fast-Setting Concrete allows you to move immediately to the next post without waiting.

Soil Bearing Capacity and Footing Size

The size of your footing is determined not just by what's above it, but by what's below it. Soil bearing capacity — the ability of soil to support a load without excessive settlement — varies significantly by soil type.

Soil Type	Bearing Capacity (psf)	Notes
Bedrock	12,000–100,000+ psf	Best possible bearing — footings can be minimal
Dense gravel / gravel-sand	3,000–8,000 psf	Good bearing — typical suburban soils
Dense sand	2,000–4,000 psf	Good — verify compaction after excavation
Loose sand / fill	500–2,000 psf	Requires wider footings or compaction
Stiff clay	1,500–4,000 psf	Watch for expansion when wet
Soft clay / peat	500–1,000 psf	High risk — may require deep footings or pilings

If you are unsure of your soil type, a licensed geotechnical engineer can conduct a soil test for $300–$800 — money well spent before pouring a large structural footing. Most local building departments will specify a minimum assumed bearing capacity (typically 1,500–2,000 psf) for residential permits; if your soil is weaker, you may need to increase footing width or switch to a different foundation system.