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Deck Footing Calculator

A deck footing calculator works out the concrete for your deck's footings — in bags and cubic yards — from the number of footings and each one's diameter and depth. Footings are the piers that carry the whole deck down to solid ground below the frost line.

Your measurements

Result

Each footing is a simple cylinder of concrete, but it's easy to under-order across six or eight of them. This totals them, gives the bag count for mixing on site, and points you at tube forms and post bases.

How it is calculated

Each footing = π × (diameter ÷ 2)² × depth. Total = that × the number of footings, converted to cubic feet and yards. Bag counts use 0.6 ft³ per 80 lb bag (0.45 ft³ per 60 lb). Footing size, depth (frost line) and spacing are set by load and local code — check span tables.

Steps

Enter the number of footings.
Enter each footing's diameter (12 in is common).
Enter the depth — below your local frost line.
Read the total concrete and the bag count.
Use tube forms for clean piers and post bases on top.

Worked example

Six 12 in diameter footings, 36 in deep, need about 0.52 cubic yards of concrete — roughly 24 bags of 80 lb mix.

Common questions

How much concrete per deck footing?

A 12 in footing 36 in deep is about 2.4 ft³ — roughly four 80 lb bags. The calculator totals all your footings.

How deep do deck footings need to be?

Below the local frost line — often 36-48 in in cold climates, shallower in warm ones. Check your building department.

Bags or ready-mix for footings?

For a handful of footings, bagged mix is convenient; for many or large piers, ready-mix or a mixer saves effort. The calculator gives both bag sizes.

What diameter footing do I need?

It depends on the load and soil — commonly 8-16 in. Use span/footing tables or an engineer for larger decks.