Deck Footing Calculator

About this calculator

A deck's footings — the concrete piers, often poured in cylindrical cardboard sonotubes, that transfer the structure's weight to undisturbed soil below the frost line — must be spaced and sized according to the beam layout and expected load, since too few or too small footings risk settling or heaving. The number needed comes from dividing the total beam span by the maximum allowable post spacing for the load, and each footing's concrete volume is simply the cylinder formula πr²h based on its diameter and depth.

This calculator takes your beam layout and footing diameter and depth, determines how many footings the deck needs, and converts the resulting concrete volume into the number of premixed bags required. DIY deck builders and residential contractors use it at the planning stage to order the right amount of concrete and confirm post spacing meets local building code before digging a single hole.