section_path: Analytic results/Circumference
section_name: Circumference
paragraph_text: Circumference
  
  The ratio of a circle's circumference to its diameter is π (pi), an irrational constant approximately equal to 3.141592654. Thus the circumference C is related to the radius r and diameter d by: C = 2 π r = π d. {\displaystyle C=2\pi r=\pi d.}