What it is
A bar chart is a column chart turned on its side. Each category gets a row with a bar whose length shows its value, all measured from the same left edge.
Turning the bars horizontal solves the most common problem with column charts: labels that collide or have to be rotated. Twenty countries, survey answers written as sentences, product names — all read naturally down the left.
✓ Use it when
- You have more than about ten categories, or labels longer than a word or two.
- You want a ranking: sorted bars read like a league table, top to bottom.
- You are showing survey results, where the options are often whole phrases.
✗ Avoid it when
- The categories are periods of time. Time reads left to right, so use columns or a line.
- You have only two or three values — the numbers themselves, in large type, may say it better.
Tips for a better chart
- Sort by value so the longest bar is on top, unless the categories have their own order.
- Keep the axis at zero, and put value labels at the end of each bar so readers don’t need gridlines.
- If labels are very long, shorten them in the data rather than letting them crowd the bars.
The maths
Exactly as for columns, a bar’s length is proportional to its value. For a ranked bar chart the order itself is information: the k-th bar is the k-th largest value, so readers can read rank and magnitude at once.
Because every bar starts from the same edge, readers compare their ends by position along a common scale — the most accurate judgement in Cleveland and McGill’s ranking, ahead of the angles and areas a pie relies on (Cleveland & McGill 1984).
A little history
Playfair’s very first bar chart was horizontal: Scotland’s trade with each partner country in a single year, published in the 1786 Commercial and Political Atlas (Playfair 1786). He chose bars because he lacked the year-by-year figures his line charts needed — a constraint that produced one of the most used charts in the world.
Questions
When should I use a bar chart instead of a column chart?
When labels are long or there are many categories. Horizontal bars give every label a full line of its own.
Why is my first category at the top?
Chart Buffet draws the first row of your table at the top, in reading order. Use “Sort” to rank the bars by value instead.
References
- Playfair, W. (1786). The Commercial and Political Atlas. London: Debrett, Robinson and Sewell.
- Cleveland, W. S. & McGill, R. (1984). Graphical perception: theory, experimentation, and application to the development of graphical methods. Journal of the American Statistical Association 79(387), 531–554.
- Friendly, M. & Denis, D. J. (2001). Milestones in the history of thematic cartography, statistical graphics, and data visualization. Web document.