Concrete Deck FootingCalculator USA — Size, Bags & Depth
Instantly calculate the correct footing diameter, concrete volume, and bags needed for wood deck posts — based on deck size, number of posts, soil bearing capacity, and frost depth per IRC 2021.
A concrete deck footing calculator for the USA helps homeowners, deck builders, and contractors determine the correct footing size, depth, and concrete bag quantity for wood deck posts — per IRC 2021 Section R507 and AWC DCA6 Prescriptive Residential Wood Deck Construction Guide. Enter your deck dimensions, number of posts, soil bearing capacity, and local frost depth, and this free tool instantly outputs the required footing diameter or side length, total concrete volume per footing, and the number of 80 lb, 60 lb, or 40 lb bags of Quikrete or Sakrete you need to purchase.
🏡 Concrete Deck Footing Calculator — USA
Enter deck size, posts, soil type & frost depth to calculate footing size, volume & bags needed.
Outer dimension of the deck platform
Outer dimension of the deck platform
Count all support posts including ledger-side posts
Check local frost depth: 0" FL · 12" GA · 36" OH · 48" MN · 60"+ AK
A concrete deck footing calculator determines the minimum required footing size and concrete volume for wood deck post supports in the USA. Under IRC 2021 Section R507.3, all deck footings must extend below the local frost depth to prevent heaving, and must be sized to distribute the post load across the available soil bearing capacity. This AWC DCA6-compliant tool handles both round Sonotube and square footings, and outputs the exact number of 40 lb, 60 lb, or 80 lb bags of Quikrete or Sakrete you need to purchase.
🔵 IRC 2021 Deck Footing Requirements at a Glance
Per IRC 2021 and AWC DCA6, deck footings must: (1) extend below the local frost depth or to undisturbed soil; (2) be a minimum of 12 inches in diameter for round footings; (3) be designed for a total design load of 40 psf live + 10 psf dead = 50 psf minimum; and (4) bear on soil with a presumptive capacity of 1,500 psf unless a soils report indicates otherwise.
🔵 Round Sonotube Footings
The most popular deck footing type in the USA. Round tube forms (Sonotube) are available in 8", 10", 12", 14", 16", and 18" diameters at Home Depot and Lowe's. A 12"×36" Sonotube footing holds approximately 2.18 cubic feet of concrete — about 4 bags of 80 lb Quikrete 5000.
⬜ Square Formed Footings
Square footings are formed with lumber or excavated by hand and are common in regions where Sonotube forms are less practical. A 12"×12"×36" square footing holds approximately 3.0 cubic feet of concrete. Square footings provide a larger bearing area per linear inch of depth compared to round footings of the same diameter.
❄️ Frost Depth by US Region
Frost depth varies dramatically across the USA: 0 in. (FL, southern TX, HI); 12–18 in. (GA, SC, LA); 24–36 in. (VA, OH, MO); 42–48 in. (NY, WI, CO); 60 in.+ (northern MN, ND, MT, AK). Always verify with your local Authority Having Jurisdiction (AHJ) before pouring.
How to Calculate Concrete Deck Footing Size — IRC 2021
The deck footing size calculation starts by finding the tributary area each post must support, multiplying by the design load to get the total post load, then dividing by the soil bearing capacity to find the required footing bearing area. Finally, back-calculate the diameter (round) or side length (square) from that area.
📐 Deck Footing Size Formula (IRC 2021 / AWC DCA6)
Tributary Area per Post (sq ft) = (Deck Area ÷ Number of Posts)
Total Post Load (lbs) = Tributary Area × Design Load (psf)
Required Bearing Area (sq ft) = Post Load ÷ Soil Bearing Capacity (psf)
⚠️ Always Extend Below Frost Depth — No Exceptions
A footing poured above the frost line will heave every winter cycle, destroying the deck structure within a few years. IRC 2021 Section R403.1.4 requires all footings to extend to below the frost line or to undisturbed soil — whichever is deeper. In northern states (MN, ND, WI, MT), this can mean footings 48"–60"+ deep. Check your local building department for the frost depth requirement before digging.
Quick-reference guide for required round footing diameters based on tributary area per post and soil bearing capacity, per AWC DCA6 Table 2 and IRC 2021 presumptive bearing values. All values assume 50 psf total design load (40 LL + 10 DL).
Tributary Area / Post
Post Load (lbs)
1,000 psf Soil
1,500 psf Soil
2,000 psf Soil
3,000 psf Soil
32 sq ft
1,600 lbs
17" dia
14" dia
12" dia
12" dia
48 sq ft
2,400 lbs
21" dia
17" dia
15" dia
12" dia
64 sq ft
3,200 lbs
24" dia
20" dia
17" dia
14" dia
80 sq ft
4,000 lbs
27" dia
22" dia
19" dia
16" dia
96 sq ft
4,800 lbs
30" dia
24" dia
21" dia
17" dia
128 sq ft
6,400 lbs
34" dia
28" dia
24" dia
20" dia
Tributary Area: 32 sq ft — Post Load: 1,600 lbs
1,000 psf Soil17" dia
1,500 psf Soil14" dia
2,000 psf Soil12" dia
3,000 psf Soil12" dia
Tributary Area: 48 sq ft — Post Load: 2,400 lbs
1,000 psf Soil21" dia
1,500 psf Soil17" dia
2,000 psf Soil15" dia
3,000 psf Soil12" dia
Tributary Area: 64 sq ft — Post Load: 3,200 lbs
1,000 psf Soil24" dia
1,500 psf Soil20" dia
2,000 psf Soil17" dia
3,000 psf Soil14" dia
Tributary Area: 80 sq ft — Post Load: 4,000 lbs
1,000 psf Soil27" dia
1,500 psf Soil22" dia
2,000 psf Soil19" dia
3,000 psf Soil16" dia
Tributary Area: 96 sq ft — Post Load: 4,800 lbs
1,000 psf Soil30" dia
1,500 psf Soil24" dia
2,000 psf Soil21" dia
3,000 psf Soil17" dia
Tributary Area: 128 sq ft — Post Load: 6,400 lbs
1,000 psf Soil34" dia
1,500 psf Soil28" dia
2,000 psf Soil24" dia
3,000 psf Soil20" dia
Pro Tips for Concrete Deck Footings in the USA
Use Quikrete 5000 or Fast-Setting concrete — Both are rated for below-grade use and footings. Quikrete Fast-Setting allows you to set posts in 20–40 minutes without mixing, which is popular for deck posts in dry conditions.
Always get a permit — Most US jurisdictions require a building permit for attached decks and decks above 30 inches off the ground. The permit process triggers a footing inspection, which protects you legally and ensures proper frost depth compliance.
Add a gravel drainage layer — Place 4 inches of compacted crushed stone at the bottom of the hole before pouring concrete. This prevents moisture accumulation under the footing, which can cause frost heave even at proper depth.
Round up to the nearest standard Sonotube size — Available diameters are typically 8", 10", 12", 14", 16", and 18". Always round your calculated diameter up to the next available tube size.
Use standoff post bases — Elevating the wood post off the concrete footing with a hot-dip galvanized post base (like Simpson Strong-Tie ABU) prevents direct wood-to-concrete contact, dramatically extending post life in wet climates.
Verify soil bearing with a simple test — If the soil looks questionable, use a pocket penetrometer or consult a local geotechnical engineer. Soft clay or fill soils may require larger footings or engineered solutions beyond the IRC prescriptive limits.
Frequently Asked Questions — Concrete Deck Footing Calculator USA
How deep do deck footings need to be in the USA?+
Per IRC 2021 Section R403.1.4, all deck footings must extend to below the local frost depth or to undisturbed soil, whichever is greater. Frost depths vary widely: 0 inches in South Florida and Hawaii; 12 inches in Georgia and South Carolina; 36 inches in Ohio and Virginia; 48 inches in Wisconsin and New York; and 60 inches or more in northern Minnesota, North Dakota, and Alaska. Always confirm with your local building department — the requirement is typically listed in your municipality's adopted code amendments.
What is the minimum deck footing size per IRC 2021?+
The IRC 2021 and AWC DCA6 prescribe a minimum footing diameter of 12 inches for round footings and a minimum side of 12 inches for square footings, regardless of the load. However, the required size may be larger based on the tributary area each post supports and your local soil bearing capacity. Most standard residential decks on 1,500 psf soil with post tributary areas under 48 sq ft can be handled with a 12"–16" diameter Sonotube footing.
How many bags of concrete do I need for deck footings?+
The number of bags depends on your footing diameter and depth. As a quick reference:
10" diameter × 36" deep: ~1.5 cu ft → 3 × 80 lb bags
12" diameter × 36" deep: ~2.2 cu ft → 4 × 80 lb bags
14" diameter × 42" deep: ~3.75 cu ft → 7 × 80 lb bags
16" diameter × 48" deep: ~5.4 cu ft → 9 × 80 lb bags
18" diameter × 48" deep: ~6.8 cu ft → 12 × 80 lb bags
Always add at least one extra bag per footing as overage. An 80 lb bag of Quikrete covers approximately 0.60 cubic feet of finished concrete.
What soil bearing capacity should I use for my deck?+
The IRC 2021 Table R401.4.1 provides presumptive soil bearing values used throughout the USA for residential construction without a soils report. The most commonly used values are: 1,500 psf (sandy loam, typical residential backyard — the default for most deck calculations); 2,000 psf (dense sand, sandy gravel); 3,000 psf (compacted gravel, gravel-sand mixtures); and 1,000 psf (soft clay, silt, or fill). If your yard has soft or expansive soil, use 1,000 psf or consult a geotechnical engineer.
Can I use Quikrete Fast-Setting concrete for deck footings?+
Yes — Quikrete Fast-Setting Concrete (No-Mix) is a popular choice for deck post footings in the USA. You simply pour dry mix into the hole around the post and add water — no mixing required. It sets in 20–40 minutes and reaches full strength in 24–48 hours. However, it is typically more expensive per cubic foot than standard Quikrete 5000. For large-diameter footings (16"+), many builders prefer mixing standard Quikrete 5000 or Sakrete High Strength for better value. Either product is code-compliant under IRC 2021.
Do I need a permit for deck footings?+
In most US jurisdictions, a building permit is required for: (1) any attached deck, regardless of height; (2) freestanding decks 30 inches or more above grade; and (3) decks on new construction. The permit triggers a footing inspection — typically before concrete is poured — to verify frost depth, diameter, and soil conditions. Skipping the permit can result in fines, required demolition, and complications when selling your home. Always contact your local building department before starting. Permit fees range from $50–$500 depending on the municipality and deck size.
What is a Sonotube and where do I buy one?+
Sonotube is a brand name for a round fiber (cardboard) concrete tube form widely used for deck footings, columns, and pier foundations in the USA. The tube holds the wet concrete in a round shape while it cures. Sonotubes are sold at Home Depot, Lowe's, Menards, and most lumber yards in diameters of 8", 10", 12", 14", 16", and 18". Standard lengths are 4 ft and 8 ft — cut to your required depth with a handsaw or reciprocating saw. After the concrete cures, peel off the fiber form above grade. Always use a form rated for ground contact (wax-coated interior).
Trusted standards, guides, and references for deck footing design and concrete compliance.
🏛️
AWC DCA6 Deck Guide
Official Standard
The American Wood Council's DCA6 Prescriptive Residential Wood Deck Construction Guide is the primary US reference for deck footing sizing, post sizing, ledger connections, and fastener schedules — fully adopted by IRC 2021 and accepted by most US building departments.
The NOAA and ICC frost depth maps show required minimum footing depths for all 50 US states. Look up your county or zip code to confirm the exact frost penetration depth required by your local building department before scheduling your footing inspection.
Quikrete's official deck footing guide covers product selection (5000, Fast-Setting, High Strength), mixing ratios, water-to-mix recommendations, curing times for footings in various US climate zones, and post base installation instructions compatible with IRC 2021 requirements.