How to Calculate a Circle

By Marina Hanes
Divide the diameter by two to get the radius.
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A circle has a center, radius and diameter. The radius is the length from the center of the circle to a point on the outside of the circle. The diameter is the radius multiplied by two. Read on to learn about how to calculate a circle.

How to Calculate the Measurements of a Circle

Place your pencil in the compass, tighten it and place the point of the instrument on the paper. Hold the point in the same place while slowly moving the pencil around the point. This will create arcs, which will later connect and create a complete circle.

Use a ruler to measure the width of the circle. This is the diameter. To find the radius, divide the size of the diameter by two. For example, if the diameter is ten then the radius is five.

Determine the circle's circumference (length of the circle's outer edge) by using the following formula: 2nr (n stands for pi, which is equal to approximately 3.14). So if the circle's radius is 5, then 2(3.14)(5) = 31.4. The circle's circumference is 31.4.

Calculate the circle's area by multiply pi by the radius squared. For example, 3.14 (5*5) = 78.5. The circle's area is 78.5.