Determine whether the data are appropriate for use in a circle graph, which must describe parts of a whole, frequency or amounts. For example, a circle graph could illustrate the type of pets owned by the students in a classroom. The data groups are the types of pets and the number of each type.
Construct a table with two columns. One column, labeled "Pet Type,"describes the parts of the whole. The other column, labeled "Number," lists the size of each sector, for example, six dogs, eight cats, four birds, one lizard and one rabbit.
Calculate the percentage of the whole that each sector makes up. There are 20 total pets, so divide the number of pets of each type by 20. Dogs: 6 ÷ 20 = 0.30, or 30 percent. Cats: 8 ÷ 20 = 0.40, or 40 percent. Birds: 4 ÷ 20 = 0.20, or 20 percent. Lizard: 1 ÷ 20 = 0.05, or 5 percent. Rabbit: 1 ÷ 20 = 0.05, or 5 percent.
Calculate the number of degrees of the circle to devote to each sector. A circle has 360 degrees, so multiply 360 by the decimal representing the proportion of each sector. Dogs: 360 x 0.30 = 108 degrees. Cats: 360 x 0.40 = 144 degrees. Birds: 360 x 0.20 = 72 degrees. Lizards: 360 x 0.05 = 18 degrees. Rabbits: 360 x 0.05 = 18 degrees.
Draw a circle using the compass. Lightly mark the center of the circle. Vertically align the center of the protractor baseline with the center of the circle. Lightly mark the 0-degree position at the top of the circle.
Mark the position of 144 degrees on the circle clockwise around the protractor from 0. Use the straight edge of the protractor to draw a straight line connecting the 0 and 144 marks to the center of the circle. This is the first sector, representing cats.
Determine the size of each remaining sector, in descending order of their proportion of the whole. Move the protractor as you work if needed.
Label each sector with the type of pet it represents and the percentage of the whole that it makes up. Or differentiate the sectors by lightly coloring them using varying colors. Or use different patterns of cross-hatching or dots for each sector.
Label the circle graph. For example, "Pets Owned by Students in the 4th Grade Class."