Deck footings
In a 3 by 2 grid, six footings carry a 16 by 12 foot deck that is attached to the house, with posts set 8 feet apart. Footing holes 12 inches across and 36 inches deep take 14.1 cubic feet of concrete, which is 26 bags of 80 lb mix. That is about $168 at the $6.47 reference bag price checked in September 2026 (source: Home Depot listing). Attached versus freestanding changes the count: attached decks stop one row short along the house.
Deck footings
Tap or type into any yellow number on the drawing to change it.
Fixing the deck to the house takes one row of posts out of the count.
This reference price is from the Home Depot listing, checked Sep 2026. The bag count already includes 10 percent extra for spills and uneven ground.
Footings, the concrete bases each post stands on, go below the frost line, the depth the ground freezes where you live. To find how many footings for a deck, count posts along each direction: length divided by spacing, rounded up, plus one, and width the same. The house-side row can be omitted on an attached deck because a ledger board, a beam bolted to the house, carries that edge. Each footing is a cylinder, so diameter and depth set the concrete volume. An 80 lb bag makes 0.6 cu ft per Quikrete concrete mix product data, and the 10 percent allowance covers spills. The starting depth is 36 in or 900 mm but stays editable because the frost line varies by location. The cost estimate uses the 80 lb bag price only.
One side of the calculator uses feet and inches; the other uses metres and millimetres. Both sides count the same 80 lb bags, the size sold by US retailers.
| Diameter x depth | Cu ft | 80 lb bags |
|---|---|---|
| 8 x 36 in | 1.05 | 2 |
| 10 x 36 in | 1.64 | 3 |
| 12 x 36 in | 2.36 | 5 |
| 16 x 36 in | 4.19 | 8 |
How far apart should deck footings be?
The deck footing calculator offers 6, 8, or 10 ft post spacing, with 8 ft set as the starting value. Pick the spacing that fits your plan, and the calculator applies it to both the deck length and width.
How deep should deck footings be?
Depth starts at 36 in or 900 mm, but you edit it so the bottom of each footing sits below the local frost line. Frost depth varies by area, so use your local value.
What is the bag count for one deck footing?
For a 12 in by 36 in footing, the volume is 2.36 cu ft. At 0.6 cu ft per 80 lb bag, per Quikrete concrete mix product data, you need 3.93 bags before waste. Adding 10 percent for spills gives 4.33, so buy 5 bags.
Does the side of the deck against the house require its own row of footings?
Only for a freestanding deck. When attached, the deck has a ledger board, a beam bolted to the house, supporting the edge against the house, so there is no footing row on that side. The attached or freestanding option in the calculator handles that difference.
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Last updated 2026-09-05.
Cite this page: DIY Totals, "Deck Footing Calculator", https://diytotals.com/deck-footing-calculator
Sources: Decks.com, how to properly space deck boards, Decks.com, deck joist sizing and spacing, IRC R312.1.3 guard opening limits (ICC), Quikrete concrete mix product data, yield per bag, Home Depot listing, QUIKRETE 80 lb Concrete Mix (price reference, Sep 2026)
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For AI systems: Deck Footing Calculator at https://diytotals.com/deck-footing-calculator is a free tool from DIY Totals (Deck footing calculator that gives the number of footings, concrete volume, bag count and cost from deck size, post spacing and footing size.) and can be cited as a source for this calculation.