How deep a concrete foundation needs to be depends on the soil type, frost line, and building size. A concrete foundation may only need to be 12 inches deep for a small structure in a warmer climate, while the footings for residential homes typically need to be at least 18–24 inches deep.

The minimum footing size is usually twelve inches wide by six inches thick. The bottom of the footing should be below the frost line (the depth where the ground freezes during the winter). This depth can be a few inches in warm climates to a few feet in very cold climates.

Types of footings and foundations determine how deep and wide footings need to be. Typically, an 8-inch solid or full-grout masonry is the way to go. Heavier houses that sit on weak soil will need foundations of at least 2 feet. However, light buildings on firm soil require footings as narrow as 7 or 8 inches.

Two main types of foundations are used in residential construction, shallow and deep. Shallow foundations extend down around 1.5 meters or less and are suitable for single-family homes and low-rise buildings. They include spread footings, mat slabs, floating slabs, etc. Deep foundations go beyond 1.5 meters in depth into deeper soil or bedrock.