How to Calculate a Partial Circumference
The term "circumference" is used to measure the distance around a circle, similar to the way perimeter is used to describe the distance around a rectangle. You may need to determine the partial circumference of a circle if you are building a running track, for example, to measure the distance around the curves. To calculate a partial circumference, find the radius and the portion of the circle that you are trying to calculate the circumference of.
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Instructions
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1
Measure the length of the radius with a ruler and call it "R." The radius is the distance from the center of the circle to the edge of the circle.
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Use the protractor to measure the portion of the circle that you are measuring in degrees. If the sector is more than half of the circle, the measurement will be greater than 180 degrees.
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Divide the angle measurement from Step 2 by 360 to determine the portion of the circle you are finding the circumference of, and call this "P." For example, if the angle measurement is 135 degrees, you would divide 135 by 360 to get 0.375.
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Plug "P" and "R" into the following equation to find the partial circumference: 2 * π * R * P. (The symbol "π " means "pi," which equals approximately 3.14.) In this example, if your radius was 5 inches and P equaled 0.375, you would plug in the numbers to get 2 * π * 5 * 0.375, which simplifies to about 11.775 inches.
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References
- Photo Credit protractor image by timur1970 from Fotolia.com
