Pie Charts
Grade 3The idea behind a pie chart
A pie chart shows how a total is split between categories. The whole circle is 360° and represents the whole data set. Each slice's angle is proportional to its share of the total.
The big trap: if the question asks you to draw a pie chart, you must work out angles first — never guess the size of a slice by eye.
The formula you need
Angle = (frequency ÷ total frequency) × 360°
Check your angles add up to 360° before you draw anything. If they don't, one of your calculations has a rounding error.
Worked example — drawing a pie chart
EXAMPLE
40 students chose their favourite subject. Maths: 10, English: 12, Science: 8, History: 10. Work out the angle for each sector.
Total = 40.
Maths: (10 ÷ 40) × 360° = 90°.
English: (12 ÷ 40) × 360° = 108°.
Science: (8 ÷ 40) × 360° = 72°.
History: (10 ÷ 40) × 360° = 90°.
Check: 90 + 108 + 72 + 90 = 360° ✓
Reading a pie chart — reverse the formula
EXAMPLE
A pie chart shows data for 60 people. The sector for "football" has an angle of 120°. How many people chose football?
Frequency = (angle ÷ 360°) × total = (120 ÷ 360) × 60 = (1/3) × 60 = 20 people.
You can only find an actual number from a pie chart if you know the total. If the question only shows the chart with no total given, you can only give proportions or percentages — not raw counts.
