Pie Charts

In a Nutshell

A pie chart shows data as sectors of a circle. Each sector angle is calculated as frequencytotal×360°\dfrac{\text{frequency}}{\text{total}} \times 360°.

A pie chart represents data as slices of a circle. The whole circle stands for the total, and each sector (slice) shows what fraction of the total belongs to that category.

To draw a pie chart, you first work out the angle for each sector. Since a full turn is 360°360°:

Sector angle=frequencytotal frequency×360°\text{Sector angle} = \frac{\text{frequency}}{\text{total frequency}} \times 360°

Then use a protractor to measure each angle from the centre of the circle. Always check that your angles add up to 360°360°.

Pie chart constructor A pie chart that updates as you change the frequency data. Each sector is labelled with its category and angle.

Watch it work

Question: 40 pupils were asked their favourite subject. Maths: 12, English: 8, Science: 14, Art: 6. Draw a pie chart.

Have a go

Q1. 20 people were surveyed. 5 chose red. What angle represents red on a pie chart?

Q2. A pie chart has a sector of 120°120°. If 60 people were surveyed, how many does this sector represent?

Q3. A pie chart has three sectors: 90°90°, 150°150°, and a third sector. What is the angle of the third sector?

Q4. Can you compare the actual frequencies of two pie charts that surveyed different numbers of people? Explain.