As a basic measurements, all footings must extend at least 1 foot into naturally untouched soil. The width of the footing depends on the size of the house.
One way to determine the load-bearing value of the soil is to refer to an index of the surface. The value is based on pounds per square foot; the highest load-bearing surface on which users can install foundations is bedrock, which has a pounds per square foot LBV of 12,000. Clay and all types of soil that contains large deposits of clay only has an LBV of 2,000, so it may not be able to support large houses.