Edit: I think the point of my question's been missed. I'm well aware pi is well defined and calculable. However my question has to do with the metaphysical, not the physical. Not how does pi work out to 3.14, but why, and how to describe the position that the why is for no reason in particular. Why C/D works out to 3.14 seems arbitrary, but arbitrary is the wrong way to describe it. Clearly I need to think about how to state my question more clearly- thanks for your answers.
Lately I've been stuck with the question of how to describe the nature of pi (and other mathematical constants), and how despite pi's definition of being C/D of a circle on the Cartesian plane, its value working out to be 3.1415... seems to be arbitrary. That is, obviously pi isn't arbitrary, because it is dependent on the properties of a circle, but it seems arbitrary that C/D turns out to be 3.1415... rather than, say, 4, or any other number.
Is there a better way to describe this observation?