Circular charts representing data as percentages or degrees.

A pie chart divides a circle into sectors to show how categories contribute to a whole. The full circle represents 100% or 360 degrees, so each sector's size is proportional to its value.

Percentages, fractions, and angles

• Percentage of a category: category value / total x 100.
• Sector angle: category value / total x 360 degrees, or category percentage x 3.6 degrees.
• Value from an angle: sector angle / 360 x total.
• Value from a percentage: percentage / 100 x total.
• Simplify ratios of categories in the same way as any other ratio.

How to interpret a pie chart

1. Identify the whole represented by the circle and its total.
2. Read the category labels and note whether values are given directly, as percentages, or as angles.
3. Convert the information to a common form before comparing categories.
4. Use the relevant percentage, angle, or value formula.
5. Check that all sectors together account for 100% or 360 degrees.

Common checks

• Every sector is part of the same whole and uses the same unit.
• Percentages should total 100%; sector angles should total 360 degrees.
• A larger sector represents a larger value, but not necessarily a larger change over time.