Deck Footing Concrete Calculator
Calculate the concrete for round deck footings from their diameter, depth and count — in cubic yards and bags.
How it works
volume per footing = π × (diameter ÷ 24)² × depth · total = per footing × count · bags = total ÷ bag yield
Each footing is a cylinder, so its volume is π × radius² × depth. Diameter is in inches, so dividing by 24 turns it into a radius in feet; multiplying by the depth (in feet) gives cubic feet. Footings must reach below the local frost line so the deck does not heave in winter — 3 to 4 feet in cold climates. Bagged mix is usually easiest here since even a dozen footings rarely reach a full yard.
Worked example
Six 12-inch footings, 3 ft deep: radius = 12 ÷ 24 = 0.5 ft, so each is π × 0.5² × 3 = 2.36 cu ft. Six of them make 14.1 cu ft, ÷ 27 = 0.52 cubic yards — about 35 eighty-pound bags with waste.
Frequently asked questions
How deep do deck footings need to be?
Below the frost line, which varies from about 12 inches in mild regions to 48 inches or more up north. Your local building department publishes the required depth; footing above it invites frost heave.
What diameter footing do I need?
It depends on the load and soil bearing capacity — 10–12 inches is common for residential decks, larger under heavy point loads. A structural table or engineer sizes it against your beam spacing and soil.
Do I need a form tube?
A cardboard form tube keeps the footing round and clean above grade and makes the concrete easy to place. Below grade in firm soil the earth itself can act as the form, but a tube is tidier and standard practice.
Related calculators
Estimates only — add for waste and confirm against local building codes and supplier specs.