The depth of a concrete foundation is typically based on the weight of the structure that it will support. A foundation should be deep enough to spread the weight of the structure over a large enough area so that the soil can support the load. The weight of a typical home is about 40 pounds per square foot, so a foundation should be at least 12 inches below ground level to support that weight. However, if there is evidence of weak or unstable soil, then a deeper foundation may be necessary.

A concrete foundation's depth depends on the weight of the building and the soil conditions. The foundation should be deep enough so that the soil can support the weight of the building. In general, a foundation should be at least twice as deep as the building's height.