It is recommended that footings in the Wisconsin area be 48" for most buildings. This is because of the deep frost that can occur in harsh Wisconsin winters.
Bldg code requirements vary with locale.
Footings will differ based upon the type of project. Most footings, if building a deck for example, should be about six feet apart.
The usual formula is this; for every foot above ground you put 1/2 foot in the ground.
This would be calculated by how much weight is above the footings.
Footing for chimneys should usually be double the width of the concrete block. For example, an 8-foot concrete block should have a 16-foot wide footing.
Footings, the concrete pads upon which foundation walls are built, must be located beneath the frost line in order to prevent a building from heaving when the ground freezes. If the site is sloped maintaining a constant elevation for the footings would either cause the footings to be above the frost line or significantly deeper than the frost line at one end of the building. Stepping the footings enables them to follow the slope of the site and remain below the frost line without going too deep under the ground. It allows the foundation wall heights to be minimized because the footings are kept as close to the surface as possible.
B/3
Generally, footings will be founded on soil or rock head below any made ground, usually on or in the first soil strata that has been established to provide suitable bearing capacity.
As long as there is a deep slope, and avalanche can occur.
Most don't get over six feet
It is a foot to the second power
Isolated footings are constructed invidually & Mat foundation is making of mat and connecting all footings with this mat