Call me π or
3.141592653589793238462643383279502884197169399375105820974944592307816406286 208998628034825342117067982148086513282306647093844609550582231725359408128481 11745028410270193852110555964

Multiply me with the diameter, and get the circumference. Take half the diameter, square it, and multiply that with me and you got yourself the full area. I'm just cool like that B)

[ Baking π's ]