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How to Calculate the Measurements of a Circle

A circle is a perfectly round two-dimensional shape. The radius represents the distance from the center to the perimeter. The diameter equals the distance from one side of the circle to the other, passing through the circle's center. The circumference equals the distance around the circle. If you know any one of these values, you can calculate the others because the ratio between the diameter and the circumference equals pi, or about 3.14.

Calculator

Instructions

- 1
  Multiply the radius by 2 to calculate the diameter. For example, if the radius equals 5, multiply 5 by 2 to find that the diameter equals 10.
- 2
  Divide the diameter by 2 to calculate the radius. In this example, divide the diameter of 10 by 2 to get 5.
- 3
  Square the radius and multiply the result by 3.14 to calculate the area of the circle. In this example, square 5 to get 25 and multiply 25 by 3.14 to get an area of 78.5.
- 4
  Multiply the radius by 6.28 to calculate the diameter. In this example, multiply 5 by 6.28 to get 31.4.
- 5
  Divide the diameter by 3.14 to calculate the diameter. Here, divide 31.4 by 3.14 to find the radius equals 10.

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