How to Calculate a Pie Graph

Pie graphs look like a pie divided up into pieces of various sizes. Each piece of pie represents some item of data with its size corresponding to the proportion that the data contributes to the whole. Calculating pie graphs is similar to calculating percentages except that instead of finding the number of parts of 100, you're finding the parts of 360 degrees. Once the math is done, you can visually represent proportions in a way that can be understood at a glance.

Things You'll Need

  • Black marker
  • Compass
  • Poster board
  • Straightedge
  • Protractor
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Instructions

    • 1

      List all the data that you want to graph, putting each item on its own line. Make the item with the greatest value the first on the list, and order the others in descending order. Find the total for all the data items, For example, data for book sales may look like:

      Suspense -- 13

      Mystery -- 11

      Romance -- 11

      Western -- 7

      Science Fiction -- 5

      Other -- 1

      Total -- 48

    • 2

      Multiply each data item by 360, and divide by the total. That quantity is the number of degrees that each section of the pie chart will take up. Write the degrees on the same line as the data item. For example:

      Suspense -- 13, 97.5

      Mystery -- 11, 82.5

      Romance -- 11, 82.5

      Western -- 7, 52.5

      Science Fiction -- 5, 37.5

      Other -- 1, 7.5

      Total -- 48, 360

    • 3

      Insert a black marker into a compass, and make a large circle on a piece of poster board. Use a straightedge and marker to draw a line from the center of the circle to the top edge of its circumference.

    • 4

      Use a protractor to mark out the angle for the first piece of pie with the number of degrees indicated on your list. The first line you drew is one side of the pie with the circle's center as the vertex of the angle. Mark the angle so that the other side of the pie is to the right of the first. Extend the angle from the center to the outer circumference of the circle with the straightedge and black marker.

    • 5

      Continue drawing pieces of pie for each item of data, working your way around the circle in a clockwise direction. Shade each piece of pie with a different color, and label them so that it's easy to see what each data item represents.

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