The Story of Pi
Now some other crazy nerds like Archimedis. What they did is , measured the circuference of the various size (big and small ) circular objects using thread . They the measured the diameter with a scale . Divided both and found it always gives a constant value = pi ,no matter how big or small circle they chose .
Thus the defination : Pi is the ratio of circumference to its diameter. i.e. Circumference / 2r = Pi => Circumference = 2r(Pi) .
Now you know that Pi was derived from Circumference and not the Vice Versa.