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Generated on: July 20, 2026 at 09:33 PM

Deck Footing Count Calculator

Inputs

Deck length6 m
Deck width3.6 m
Max footing spacing2.4 m

This is a simple grid estimate, not a structural design. The real footing layout depends on the beam and joist spans, the load, soil bearing, frost depth, ledger attachment, stairs, and cantilevers. Footing size, depth, and spacing for a deck must follow local code and, where required, an approved plan or inspection.

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Construction & DIY

Deck Footing Count Calculator

Lay out a grid of footings under a rectangular deck so no span exceeds a chosen maximum spacing, and get the total number of footings to dig and pour.

Inputs

≥ 0 m
≥ 0 m
≥ 0 m

Results

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Details

A 6 m × 3.6 m deck needs about ... footings — ... along the length by ... across the width.

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Deck Footing Count

A deck stands on footings, and the footings are laid out in a grid so no span between them exceeds what the beams and joists can safely carry. This calculator turns the deck size and a maximum spacing into the number of footings along each side and the grid total.

Counting the grid

Along each direction the number of spans is the deck dimension divided by the maximum spacing, rounded up, and the number of footings is one more than the spans because the row starts and ends on a footing:

nL=⌊Ls⌋+1nW=⌊Ws⌋+1\begin{aligned} n_L &= \left\lfloor \frac{L}{s} \right\rfloor + 1 \\ n_W &= \left\lfloor \frac{W}{s} \right\rfloor + 1 \end{aligned}

The grid total is the product of the two directions:

N=nL nW\begin{aligned} N &= n_L \, n_W \end{aligned}

The floor of the division plus one is used so that a span landing exactly on the spacing does not add an extra footing prematurely; the result places a footing at every corner.

Worked example

Consider a 6 × 3.6 m deck with a maximum footing spacing of 2.4 m:

nL=⌊62.4⌋+1=2+1=3nW=⌊3.62.4⌋+1=1+1=2N=3×2=6\begin{aligned} n_L &= \left\lfloor \frac{6}{2.4} \right\rfloor + 1 = 2 + 1 = 3 \\ n_W &= \left\lfloor \frac{3.6}{2.4} \right\rfloor + 1 = 1 + 1 = 2 \\ N &= 3 \times 2 = 6 \end{aligned}

So the deck needs about 6 footings.

Consider a 20 × 12 ft deck with a maximum footing spacing of 8 ft:

nL=⌊208⌋+1=2+1=3nW=⌊128⌋+1=1+1=2N=3×2=6\begin{aligned} n_L &= \left\lfloor \frac{20}{8} \right\rfloor + 1 = 2 + 1 = 3 \\ n_W &= \left\lfloor \frac{12}{8} \right\rfloor + 1 = 1 + 1 = 2 \\ N &= 3 \times 2 = 6 \end{aligned}

So the deck needs about 6 footings.

Choosing inputs

The maximum spacing is the structural input, set by how far your beams and joists can span for their size and species — not by a single fixed number. Many residential decks land near 2.4 m (8 ft) between footings, but larger beams reach further and heavier loads pull them closer, so take the value from a span table or an approved plan. Cantilevers, stairs, and beams that run past the last post can shift or add footings beyond this simple grid.

For the concrete to pour each footing, see Post-Hole Concrete Calculator.

Frequently Asked Questions (FAQ)

How many footings does my deck need?

Divide each deck dimension by the maximum spacing, round up to get the number of spans, and add one for the footing at the far end. Multiply the two directions for the grid total. A 6 × 3.6 m deck with a 2.4 m maximum spacing works out to 3 footings along the length by 2 across the width, so 6 footings. The real number can be higher near the house or under heavy point loads.

How far apart should deck footings be?

The spacing is set by how far the beams and joists can span for their size and species, not by a single fixed number. Many residential decks land near 2.4 m (8 ft) between footings, but larger joists span further and heavier loads need them closer. Use the beam and joist span tables in your local code or your approved plan to choose the maximum spacing to enter here.

Do footings go on the corners?

Yes. Because the count adds one footing past the last span in each direction, the grid includes a footing at every corner and at the ends of every beam line. Cantilevered decks, stairs, and beams that run past the last post can shift or add footings, so treat this grid as a starting layout and confirm it against your beam design.

Disclaimer

This is a simple grid estimate, not a structural design. The real footing layout depends on the beam and joist spans, the load, soil bearing, frost depth, ledger attachment, stairs, and cantilevers. Footing size, depth, and spacing for a deck must follow local code and, where required, an approved plan or inspection.

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