Pie Chart Calculator

A pie chart shows how parts make up a whole. Enter your categories and numbers and this calculator works out each slice’s percentage and angle, draws a labelled pie or donut chart, and lets you download it — plus the step-by-step working for homework or reports.

How to calculate a pie chart

1. Add up all the values to get the total.
2. For each category, divide its value by the total.
3. Multiply by 100 to get its percentage.
4. Multiply by 360 to get the angle of its slice in degrees.
5. Draw each slice with a protractor, starting from a vertical line and going clockwise.

The angles always add up to 360° and the percentages to 100% (allowing for rounding).

Worked example

A monthly budget of $2650: rent is 1200 ÷ 2650 = 0.4528 of the total, which is 45.3% and 163.0° of the circle. These are the default values in the calculator.

When to use a pie chart

• The categories are parts of one whole (they add up to 100%).
• There are only a few categories — about six or fewer is easiest to read.
• You want to show that one part dominates, or compare a part with the whole.
• Values are all positive.

When to choose something else

People judge angles and areas less precisely than lengths, so for close comparisons a bar chart is usually clearer.

Drawing a pie chart by hand

1. Draw a circle with a compass and mark the centre.
2. Draw a radius straight up from the centre to 12 o’clock.
3. Place the protractor’s centre on the circle’s centre, aligned with that radius.
4. Measure the first angle clockwise and draw the next radius.
5. Move the protractor to the new radius and measure the next angle — or add angles cumulatively from the first line.
6. Label each slice or add a key, and check the last slice fills the remaining angle.

Cumulative angles reduce errors: for the worked example, draw lines at 163.0°, 224.2°, 251.3°, 271.7°, 326.0° from the starting line.

Reading a pie chart

To turn a slice back into a number, multiply its percentage by the total: if a survey of 250 people shows 18% chose “walk”, that is 0.18 × 250 = 45 people. To find a percentage from an angle, divide by 360: a 72° slice is 72 ÷ 360 = 20% of the whole. Exam questions often combine the two — measure the angle with a protractor, convert to a fraction of 360, then multiply by the total given in the question.

Common mistakes

• Using values that don’t form a whole, such as scores from different tests.
• Forgetting to multiply by 360 (or by 100) after dividing by the total.
• Rounding angles too early so the slices don’t add to 360°.
• Too many tiny slices that can’t be labelled.
• Using 3-D effects or exploded slices that distort proportions.

Pie vs donut

A donut chart is a pie chart with the centre removed, which leaves room for a total or a label. It reads the same way. Avoid 3-D pie charts: tilting the circle distorts the slices, making front slices look bigger than they are.

Pie charts in spreadsheets

In Excel or Google Sheets, put category names in one column and values in the next, select both and insert a pie chart. The chart calculates the percentages for you; right-click the slices to add data labels showing percentages or values. To match the calculator’s working, add a column with =B2/SUM(B:B) for the fraction and multiply by 360 for degrees — the template pack includes a ready-made version with these formulas.

Pie charts in school maths

Curricula differ; these are common stages rather than requirements.

Tips for clear pie charts

• Sort slices from largest to smallest, starting at 12 o’clock.
• Combine very small slices into “Other”.
• Label slices directly or with a clear legend.
• Use distinct colours with enough contrast.
• State the total and the date or source of the data.

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