In-ground base foundation
You didn't mention what is the foundation to support, a patio with deck is very different from a 2-stories building in concern of settlement tolerance.
The settlement is a function of soil bearing strength and footing area, for a concentrically loaded foundation, the bearing pressure is the total force (superimposed dead load + live load + footing self-weight) divided by the footing area, the resulting bearing pressure must not exceed the allowable bearing strength. For the dry condition, you can obtain the presumptive bearing pressure from the building code, or from the local building department provided that you know the type of the underlying soil. However, if there is the presence of groundwater near or above the bottom of the footing, you shall consult a geotechnical engineer for guidance.