Definition
A footing is the lowest part of a foundation system that spreads the structural load from the building into the supporting soil. Footings are typically made of reinforced concrete and are wider than the foundation walls or columns they support, distributing weight to prevent settling or foundation failure.
Formula
The required footing size depends on the building weight (load) and the soil's bearing capacity. Typical residential footings are 12-24 inches wide and 6-12 inches thick.
Example
Residential Footing Example
For a typical home with a load of 40,000 lbs and soil bearing capacity of 2,000 psf (pounds per square foot), you need a footing area of 20 square feet. If the footing runs 40 feet long, it needs to be at least 6 inches wide. Standard practice uses 16-inch wide footings to provide a safety margin.