How many square feet in a foot?

Answer 1

None. A foot is a measure of distance, a square foot is a measure of area.
This question cannot be answered sensibly. A square foot is a measure of area, with dimensions [L2]. A foot is a measure of distance, with dimensions [L]. The two measure different things and basic dimensional analysis teaches that you cannot convert between measures with different dimensions such as these without additional information.
A foot is a measurement of distance. That is to say it is measuring how far it is from point A to point B.

A square foot is a measurement of area.

Distance and area are not the same thing. It is a little like asking how many hours are there in a foot, in the sense that the question does not make sense and thus has no answer.

Answer 2

A square foot is an area 1' x 1'