Charts
Pie Chart Maker
Parts of one whole, drawn as slices — with the percentages printed, because angles are hard to judge.
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How to read this result
A pie chart answers one question well: what share is this of the whole? For anything else — comparing similar slices, showing change over time, ranking categories — a bar chart is better, and that is not a matter of taste. People judge lengths accurately and angles poorly.
Keep it to a handful of slices. Past about six or seven, the wedges become too similar to compare and the labels start to collide. The calculator warns when there are more.
Every slice must be part of the same total. If the categories overlap, or if they do not add up to a meaningful whole, a pie chart asserts something false about the data.
Percentages are printed on the chart because reading a value off an angle is not reliable — and the full table sits underneath for the same reason.
Negative values are impossible here. A slice with negative area has no meaning, so the calculator refuses them and points you at a bar chart.
The formula
Each slice's share of the whole, converted to degrees. A 25% slice is a right angle — the only proportion most people can judge accurately by eye.
Worked example
Traffic by source
Where a month's visits came from: 50% search, 30% direct, 20% social. Three slices, one whole, no overlap — the situation a pie chart actually suits.
Search 500, Direct 300, Social 200
- Total the values.500 + 300 + 200 = 1,000
- Each slice's share.50%, 30%, 20%
- Convert to degrees.180°, 108°, 72°
- Sort largest first so the wedges are easier to compare.search, direct, social
Three slices with a clear ordering is close to the only case where a pie chart beats a bar chart — the 50% slice is instantly recognisable as half, which is the one judgement people make reliably from an angle.
Checked against arithmetic.
The calculator above is loaded with these numbers by the Load the worked example button.
Assumptions, and when to use something else
The categories must be mutually exclusive and jointly make up a meaningful whole, and every value must be positive. Pie charts of percentages that do not sum to 100, or of overlapping categories, are asserting something the data do not support.
Beyond that the limits are perceptual rather than statistical: comparing two slices of similar size, or comparing across two pie charts, is a task people perform poorly, and no amount of styling fixes it.
- You have more than about six categoriesBar chart makerLengths are far easier to compare than angles.
- Any value can be negativeBar chart makerA negative slice has no meaning.
- You want to show change over timeLine graph makerTwo pie charts side by side make change almost impossible to read.
Questions people ask
When should I not use a pie chart?
When there are more than about six categories, when the slices are similar in size, when you need to compare across two charts, when values can be negative, or when the categories are not parts of one whole. A bar chart handles all of those better.
Should slices be sorted?
Yes, largest first, starting at twelve o'clock. It makes the ordering readable and puts the biggest wedge in the position people look at first. The calculator does this automatically.
Is a donut chart better than a pie chart?
Marginally. Removing the centre focuses attention on arc length rather than area, which people judge slightly better, and the hole is useful space for the total. Neither fixes the fundamental problem of comparing angles.
How do I download the chart?
Every chart draws to a canvas in your browser. Use the download button for a PNG, or right-click the image and save it. Nothing is uploaded to produce it.