1The whole circle is 100%
A pie chart shows all your survey data as a single circle. The whole circle stands for 100%, and each category gets sliced out as a wedge sized to match its share. It's a lot like cutting a single cake into several pieces.
2Percentage = (part) ÷ (whole) × 100
If 8 out of 20 people say summer is their favorite, you find the percentage by dividing 8 by 20 and multiplying by 100.
40% of everyone surveyed prefers summer.
3Central angle = percentage × 3.6°
A full circle is 360 degrees. Since 100% corresponds to 360 degrees, 1% works out to 3.6 degrees (360÷100). So to find any category's central angle, just multiply its percentage by 3.6.
The wedge representing summer has a central angle of 144 degrees.
On the activity page's table, check that adding up every category's percentage gives 100%, and adding up every central angle gives 360°.
4How is this different from a bar graph?
A bar graph is great for comparing category sizes by bar length, while a pie chart is great for seeing at a glance what share each category takes up of the whole. When you're wondering "what percent of the class does this category make up?", a pie chart is the better fit.
5Try this
- Increase the count for one category. Check how its wedge, percentage, and central angle all grow together.
- Make every category the same size. Check that four equal categories each split into 25% and 90°.
- Try a different survey topic. See that the same idea applies just as well to other data — favorite sport, blood type, anything else.