Which chart for which data: the decision grid
Nine questions, nine answers. Pick charts by what you are asking the data, not by what looks impressive. Free print-ready PDF.
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Chart choice is not aesthetic, it is grammatical: each chart type answers one kind of question. Ask the question first, and the chart picks itself.
The decision grid
| The question | The chart | The note |
|---|---|---|
| How did it change over time? | Line chart | time on x, always |
| How do categories compare? | Bar chart | horizontal when labels are long |
| What are the parts of a whole? | Stacked bar | pie only with 4 slices or fewer |
| How is one variable spread out? | Histogram | bin width changes the story |
| Are these two things related? | Scatter plot | add a trend line, never a dual axis |
| What is the ranking? | Ordered bar | sort by value, not alphabet |
| Trend and volume together? | Area chart | one series, or it turns to mud |
| One number that matters? | Big number | plus the change vs last period |
| Two categories crossed? | Heatmap | let the color scale do the work |
The trap: the 12-slice pie
Past 4 slices nobody compares the angles. Past 6 it is decoration. The same data as an ordered bar reads instantly. And the dual axis is worse: two scales, one lie; split the charts instead.
If you must show share of total: top 3 slices + "other", or an ordered bar.
Bar or line?
The most common hesitation, settled:
Bar when: comparing categories, discrete periods (Q1 vs Q2), rankings and top-N, long labels (go horizontal).
Line when: continuous time, many points and one trend, up to 4 series, rates and indexes.
Safe defaults
- In doubt? Bar chart. It is almost never wrong.
- Colors: one accent, grey the rest. Highlight the answer.
- Axis at zero: bars always. Lines may zoom, but say so.
- 3D charts: no. Not once. Not for the CEO either.
Frequently asked questions
- When is a pie chart OK?
- With four slices or fewer, when the point is a rough share of a whole. Beyond that, angles become impossible to compare: use an ordered bar, or show the top 3 slices plus an 'other' bucket.
- Should I use a line chart or a bar chart?
- Line for continuous time and trends; bar for comparing categories or discrete periods like Q1 vs Q2. If the x-axis is not time or another continuum, a line falsely implies a connection between points.
- How do I show two measures on one chart?
- Avoid the dual axis: two scales invite misreading and can be tuned to tell any story. Use two small stacked charts sharing the x-axis, or plot the relationship directly with a scatter.
- What is the best chart for survey results?
- Usually an ordered horizontal bar: categories sorted by value, long labels readable. For Likert scales, a diverging stacked bar centered on the neutral point works well.
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