How to Calculate Area of a Semi Circle

Written by michael keenan
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How to Calculate Area of a Semi Circle
A semicircle equals half of a circle. (Hemera Technologies/ Images)

A circle is a round shape with each point equally far from the centre. When finding the area of a semicircle, the easiest way to proceed is to find the area of a full circle and divide by two, because a semicircle equals half of a full circle. You might need to know the area of a semicircle if you are painting a design or a sign and you need to know the size of the area you need to cover.

Skill level:
Moderately Easy

Things you need

  • Ruler
  • Calculator

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  1. 1

    Measure the distance from one side of the circle to the other, passing through the circle centre. This is the diameter.

  2. 2

    Divide the diameter by 2 to find the radius of the semicircle. For example, if you have a diameter of 14 inches, you would divide 14 by 2 to get 7 inches.

  3. 3

    Square the radius. In this example, the radius equals 7 inches, so you would multiply 7 inches by 7 inches to get 49 square inches.

  4. 4

    Multiply the answer in Step 3 answer by 3.14 (the value of pi) to find the area of a full circle. In this example, you would multiply 49 square inches by 3.14 to get 153.86 square inches.

  5. 5

    Divide the area of the full circle by 2 to find the area of the semicircle. Completing the example, you would divide 153.86 square inches by 2 to find that the area of the semicircle equals 76.93 square inches.

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