What is a good rule of thumb for sizing footings in light construction?

A good rule of thumb for sizing footings in light construction is to ensure that the footing width is at least twice the width of the supporting wall or column it is under. Additionally, the footing depth should be at least 12 inches or below the frost line, whichever is greater, to prevent settling and frost heave. Always consider local building codes and soil conditions, as they can significantly affect the required sizes.