Circle Graphs
Circle graphs are used to represent a “part” to “whole” relationship for categorical data.
The full circle represents the whole and each sector represents the part corresponding to the
categorical data.
Constructing Circle Graphs
Steps:
1. Is the data suitable?
• Determine if there is a “whole” for the data.
• Determine what the different parts of the whole are.
2. Calculate the fractions, decimals, and/or percent for each category
• Divide (part ÷ whole) to create a fraction.
(You can choose to work with the fraction, or you can divide to change the
fraction to a decimal. Once you have a decimal, you can also divide by 100 to
change to a percent.)
In general, it is easiest to use fractions if you do not have a calculator and decimals if
you do have a calculator.
3. Convert each fraction, decimal, or percent to an angle of the circle.
• Without a calculator, multiply the fraction by 360 to find the central angle.
(there are 360° in a circle and we are trying to find the fraction of the circle that
represents each category)
• With a calculator, multiply the decimal by 360 to find the central angle.
(if you are using percent, it is best to change to a decimal first and then multiply
by 360)
4. Use a protractor to measure the angle for each sector as accurately as possible.
• Start with a radius drawn anywhere.
• Measure the angle of the first sector starting at the radius drawn.
• All subsequent sectors should be drawn adjacent to the previous sector drawn.
• The last sector should be measured to check for accuracy.
What are the three necessary skills to create circle graphs?
Changing data to fractions, decimals, and percent. (complete the table)
Brand Name
Number Sold
Adidas
150
Nike
192
Reebok
60
Asics
108
Other
90
To create a fraction remember
Fraction
Reduced
Fraction
Decimal
Percent
part
whole
There were 600 pairs of sneakers sold, so for Adidas:
150
600
To reduce the fraction, divide the numerator and denominator by the same number.
150 10 15 15 1


600 10 60 15 4
To change to a decimal, simply use a calculator to divide 150  600  0.25
To change the decimal to a percent, move the decimal two places to the right.
or
1  4  0.25
Next we need to change each fraction, decimal or percent to an angle.


Recall that a circle contains 360◦.
Each sector of the circle will represent a fraction of the whole circle.
To find the angle of the sector representing Adidas, recall the following information.
Brand
Name
Number
Sold
Adidas
150
Fraction
150
600
Reduced
Fraction
1
4
Decimal
Percent
0.25
25%
Below, show work on how to find the angle that will form the sector representing Adidas.
By hand
with a calculator
Find the angle representing each sector of the circle graph. (show work)
Measure the following angles with a protractor:
Draw the following angles using a protractor.
45o
133o
330o