Deck Footing & Concrete Calculator
Work out how many footings your deck needs and how much concrete to buy — in footings, cubic feet, cubic yards, and bags.
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How many footings does a deck need?
Footings sit under each post along your beams. Space posts no more than about 8 feet apart on center, then add one footing at each end of every beam row. Larger beams and bigger loads allow wider spacing — check your local code and span tables.
How much concrete per footing?
A footing is a cylinder: volume = π × radius² × depth. A 12"-diameter footing poured 42" deep takes about 2.7 cubic feet — roughly six 60-lb bags. Always dig footings below your local frost line so they don’t heave.
Frequently asked questions
- How deep should deck footings be?
- Below the frost line for your area — often 36"–48" in cold climates, shallower in warm ones. Your building department sets the requirement.
- How many 60-lb bags make a cubic yard?
- About 60 bags. A 60-lb bag yields ~0.45 cubic feet, and there are 27 cubic feet in a yard.
Next steps
- Deck Cost Calculator — total project price.
- Deck Board Calculator — boards and screws.
- Stairs Calculator — risers, treads, stringers.