In reply to daniel wanjiru.

Good question, Daniel.
We can't apply the same logic to the circumference as long as both, circumference and diameter are measured in the same linear units of length. Therefore, π is a "king" there, as it represents a fundamental constant - the ratio circumference/diameter. In case of areas (volumes) we can vary definitions of the gauge thus arriving at different formulas.
However, if we measure length in non-linear units (e.g. logarithmic scale) then we can arrive at various circumference formulas.