A pie chart is a circular graph divided into slices, like a cake cut into pieces. It is used to show how a whole is shared out into different parts. Each slice shows the proportion, or share, of the total taken by one category.
How a Pie Chart Works
The complete circle represents 100% of the data, and a full circle measures 360°. The size of each slice depends on the fraction of the total it stands for. A bigger slice means a bigger share; a small slice means a small share. Pie charts are best when you have only a few categories.
Key idea
Angle of a slice = (value of category ÷ total value) × 360°. All the slices together add up to 360°, or 100%.
Example
If 25% of a district's land is used for oil palm, that slice has an angle of 0.25 × 360° = 90°, exactly one quarter of the circle.
Reading and Drawing
To draw a pie chart you need a compass, a protractor to measure the angles, and colours or shading to separate the slices. Always give the chart a title and a legend (key) so the reader knows what each slice means.
Remember
- Whole circle = 360° = 100%.
- Larger slice = larger proportion.
- Include a title and a legend.
Pie charts clearly show which category is largest or smallest, but they do not show change over time and become confusing with too many small slices.