How to Calculate Circumference and Diameter of Circle

Updated February 21, 2017

The circumference of a circle is the distance around its perimeter, and the diameter is the distance across the circle through its centre. Figuring circumference and diameter is a task that usually is taught in middle school and also is used in high school and college geometry. Real-life applications of these measurements can be found in careers such as landscaping and engineering.

If the circle is drawn to scale, measure a straight line crossing through the centre of the circle, from one end of the circle to the other, to get the diameter.

The radius is the line from the centre of the circle to the perimeter. Multiply the radius by two if the radius measurement is provided to get the diameter. For instance, if the radius is three, the diameter would be six.

Divide the circumference by pi (3.14) if the circumference measurement is given. For example, if the circumference is 10, divide 10 by 3.14 to get a diameter of 3.1847.

Obtain the diameter of the circle. This information may be given, or you may have to use a ruler to measure a line through the centre of the circle to get the diameter.

Again, multiply the radius times two to find the diameter in cases where the radius measurement is provided.

Multiply the diameter times pi (3.14) to find the circumference of the circle. For instance, if the diameter is three inches, multiply 3 times 3.14 to get a circumference of 9.42 inches.

Things You'll Need

  • Ruler or tape measure
  • Calculator
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About the Author

Charlotte Johnson is a musician, teacher and writer with a master's degree in education. She has contributed to a variety of websites, specializing in health, education, the arts, home and garden, animals and parenting.