Deck Footing Concrete Calculator

How to Use This Deck Footing Concrete Calculator

Use this deck footing concrete calculator to estimate the total concrete volume and bag count for any type of deck footing. Choose your footing shape — round pier (sonotube), square or rectangular pad, Bigfoot bell-bottom form, or enter a known area — then input the dimensions and quantity. The calculator returns instant results in cubic yards, cubic feet, bags needed, and an optional cost estimate. For continuous strip footings, see our concrete footing calculator.

How to Calculate Concrete for Deck Footings

The formula depends on the footing shape:

Round Pier (Sonotube)

Volume = pi x (Diameter / 2)² x Depth

Multiply by the number of piers, then divide cubic feet by 27 for cubic yards.

Square / Rectangular Pad

Volume = Length x Width x Depth

Common for hand-dug footings or form-built pads under deck posts.

Bigfoot Form

Bigfoot forms are bell-shaped plastic bases (BF-20, BF-24, BF-28, BF-36) placed below a cardboard tube. Total concrete = bell form volume + tube cylinder volume above it.

Step-by-Step Example (Round Pier)

1. Measure the footing diameter — most residential decks use 12-inch (1 ft) sonotubes
2. Determine the depth below grade — check your local frost depth (e.g. 36 inches in the Midwest)
3. Count the number of piers — a 12×16 ft deck typically needs 6–9 footings
4. For 8 piers at 12 in diameter × 36 in depth: each pier = 0.785 × 1² × 3 = 2.36 ft³
5. Total = 2.36 × 8 = 18.85 ft³ = 0.70 cubic yards
6. Add 10% waste: 0.77 cubic yards — about 52 bags (60 lb)

How Many Footings Does a Deck Need?

The number of footings depends on your deck design, joist span, and beam layout. General guidelines:

• Small deck (10×12 ft) — 4–6 footings
• Medium deck (12×16 ft) — 6–9 footings
• Large deck (16×20 ft) — 9–12 footings
• Multi-level or wrap-around — 12–20+ footings

Place footings every 6–8 feet along each beam, plus at every corner and stair landing. Your deck plan or local building department will specify the exact number and spacing. Use the quantity field in the calculator above to enter your total pier count.

Deck Footing Depth and Frost Line

Footings must extend below the frost line to prevent frost heave from pushing posts out of the ground. Frost depth varies widely by region:

• Southern states (FL, TX, LA) — 6–12 inches (some areas have no frost requirement)
• Mid-Atlantic (VA, NC, TN) — 18–24 inches
• Midwest (OH, IL, IN) — 36–42 inches
• Northern states (MN, WI, ME) — 42–60 inches

Always check your local building code for the exact frost depth. Digging 6 inches deeper than the minimum requirement provides a safety margin. For more details on footing depth, see our concrete footing calculator.

Tips for Pouring Deck Footings

• Use sonotubes for clean piers — cardboard form tubes keep the concrete round and prevent soil from mixing into the pour; standard sizes are 10, 12, and 14 inches
• Extend the tube above grade — raise the sonotube 2–4 inches above the soil line to keep the wood post dry and prevent rot at the base
• Set post brackets before the concrete sets — push a galvanized post base bracket into the wet concrete and plumb it immediately; this creates a stronger connection than drilling after the pour
• Flare the bottom for extra bearing — for heavy loads, dig a wider bell at the bottom of the hole (e.g. 18 inches wide at the base of a 12-inch tube) to spread the load over more soil
• Order 10% extra concrete — always add a waste factor for spillage, uneven holes, and slightly oversize pours