Pie charts (sometimes called circle graphs) are used to compare data. Slices of different size are marked on a circle (i.e. the pie) based on what part of the whole they represent. The pie chart example below illustrates this.
Example of a Pie Chart
The pie chart below shows the Carbon Dioxide (CO2) emissions in California.
CO2emissions in California by consumption sector. Source: http://www.giss.nasa.gov/meetings/pollution2002/summaryd.html
How to Make a Pie Chart
Pie charts show a fraction of a circle that is the same fraction as is the quantity being represented is of the whole amount. Think of a group of 4 children where 1 is left-handed and the other 3 are right-handed. The pie chart showing this would look like the second example below:
1 out of 4 students is left-handed. This is one-fourth of the whole group.
3 out of 4 students are right-handed. This is three-fourths of the whole group.
This example is quite simple; a pie chart probably is not even needed to show the relationship between the number of left-handed and the number of right-handed students. The example below is a better one.
The third example of a pie chart shown below shows time use on an average weekday for full-time university and college students in the U.S.A.
The table below shows how the size of the slices and their angles are calculated for the above pie chart.
|1||Find the total of all the parts.
Note: In this example we are given the total but that is not always the case
|8.3 + 3.6 + 3.3 + 3.0 + 2.5 + 1.5 + 1.0 + 0.8 = 24.0|
|2||Write the fraction of the total for the first part (Hours sleeping)||8.3/24.0|
|3||Write the fraction as a decimal.
In other words, divide the numerator by the denominator
|8.3 ÷ 24.0 = 0.3458|
|4||Multiply the decimal by 360° to find the angle for the slice that will show this part.||0.3458 x 360° = 124.5°|
|Below you can see what we have just calculated.|
|5||Repeat Steps 2 to 4
for all the other parts
|Leisure and sports
= 0.15 x 360° = 54°
3.3/ 24.0 = 0.1375 x 360° = 49.5°
3.0= 0.125 x 360° = 45°24.0
2.5/ 24.0 = 0.1042 x 360° = 37.5°
1.5= 0.0625 x 360° = 22.5°24.0
|Eating and drinking
1.0/ 24.0 = 0.0417 x 360° = 15°
0.8= 0.0333 x 360° = 12°24.0
|6||Check the angles add up to 360. (note: there could be rounding errors and the total might not be exactly 360.||124.5 + 54 + 49.5 + 45 + 37.5 + 22.5 + 15 + 12 = 360°|
Draw the slices on the pie chart.
Pie Chart Worksheets
The three worksheets below will provide practice with calculating the angles that are used to create pie charts.
More help with making pie charts
Check out this great web site where you can create many different pie charts and other types of chart too.
Remember that there are situations where pie charts are not a good way to show relationships between data. For example, if the quantities involved are quite similar and/or there a large number of sectors, the resulting chart can be a poor way of showing the information. In such cases, a table or other type of chart is often a better choice.