🥧 Pie Charts

A pie chart is a circular graph divided into slices to represent data. It looks similar to a pizza cut into pieces.

Each slice shows a proportion of the whole, and the values are expressed as percentages.

Pie charts are useful when we want to show how different categories contribute to a total.

📊 Key Features of Pie Charts

  • ✔️ The graph is circular
  • ✔️ The entire circle represents 100% of the data
  • ✔️ Each slice represents a category
  • ✔️ Slice size shows how large that category is compared to the whole
  • ✔️ Values are shown as percentages or degrees
Unlike bar charts, pie charts emphasize proportions rather than exact comparisons.

🏀 Example: Jacket Sizes for a Basketball Team

A girls’ basketball team is ordering jackets for the Regional Championship. The head coach wants to show the distribution of jacket sizes using a pie chart.

Step 1 — Organize Data into a Table

Jacket Size Frequency (Number of Players)
Extra Small5
Small10
Medium26
Large19

Adding the frequencies gives the total number of players:

5 + 10 + 26 + 19 = 60 players

📐 Step 2 — Convert Frequencies to Degrees

A full circle contains 360 degrees.

To find how many degrees each player represents:

360° ÷ 60 players = 6° per player

Now multiply 6° by the number of players in each category:

  • Extra Small: 6 × 5 = 30°
  • Small: 6 × 10 = 60°
  • Medium: 6 × 26 = 156°
  • Large: 6 × 19 = 114°

✔️ Check the Total

30° + 60° + 156° + 114° = 360° ✓

Since the total equals 360°, the calculations are correct.

📊 Step 3 — Convert to Percentages

The entire pie represents 100% of the players.

To find the percentage each player represents:

100% ÷ 60 players ≈ 1.7% per player

Now multiply 1.7% by each frequency:

  • Extra Small: 1.7 × 5 = 8.5%
  • Small: 1.7 × 10 = 17%
  • Medium: 1.7 × 26 = 44.2%
  • Large: 1.7 × 19 = 32.3%
The total should be approximately 100%. Small differences happen due to rounding decimals.

✏️ Step 4 — Drawing the Pie Chart

  • Draw a large circle using a compass or protractor
  • Measure each angle from the center using a protractor
  • Draw slices based on calculated degrees

Slice Measurements:

  • Extra Small → 30°
  • Small → 60°
  • Medium → 156°
  • Large → 114°

Finally, label each slice with its percentage to make the chart easier to read.

✅ Why Pie Charts Are Useful

  • They clearly show proportions of a whole
  • They are visually simple and attractive
  • They help identify the largest and smallest categories
  • They are useful for surveys and population data
  • They make percentage data easy to understand
Pie charts are best used when showing how data is divided among categories that make up a whole.
Pie charts transform numerical data into visual proportions, making percentage comparisons simple.