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    Circumference of a Circle

    Formula for circumference with examples


    The circumference of a circle is the edge or rim of a circle itself. It is the equivalent of 'perimeter' for a circle. In other words, if you took a circle and unrolled it, you would have its circumference. You can use either of the formulas below to find circumference of a circle. One formula use the radius of a circle; the other formula uses the diameter.

    • Formula for Circumference

      = 2Πr where r is the radius of a circle.
    • alternately,
      circumference Formula
      = d• Π where d is the diameter of a circle.
      • **These two formulas are just two different ways of finding the same thing (circumference) because the diameter of a circle =2• radius. So you should make use of whichever formula is more convenient. If you know a circle's radius, use the first version of the formula; if you know the diameter, use the second.
    This Page: Practice Problems | circumference formula
    Related Pages: Standard Form Equation for a Circle | Chord of Circle| Tangent to a Circle |Arc | Inscribed Angles

    The rotating line on the left is an example of a circle's radius.


    If the radius of a circle is 1 inch (1"), then the circumference of the circle = 2Π• 1" ≈   6.28"


    Practice Problems

    Problem 1) What is the circumference of the circle below.
    circumference
      Circumference  


    Problem 2) What is the circle's circumference?
    circumference of 9 inch circle   Circumference  
    Problem 3) What is the circumference of the circle pictured below?
    circumference practice problem   Circumference  
    Problem 4) What is the circumference of a circle with a radius of 5"?
      Circumference  
    Practice Problems (Medium)


    Problem 5) A circle's circumference is (22Π)". What is the radius of this circle?
      radius  
    Problem 6) A circle's circumference is (102Π)". What is the diameter of the circle?
      diameter   circumference = 2Π•r = d×Π= 102 Π"
    d = (102Π")/Π = 102"
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