The circular mil is a unit designed specifically to measure the area of a wire with a circular cross section. It has the symbol cmil.
An inch is 1000 mils. This makes the circular mil particularly useful for measuring cross sections of wire as there is no need to use the symbol π so the process is simplified.
A circular mil is a very small unit so not advised to use for large areas!
The square foot is a unit of area and is an imperial unit with the symbol ft².
One square foot is equal in area to a square with edges one foot in length.
It is used a lot in expressing the internal size of a house, apartment, office or other properties so is a useful unit to understand.