Definition
A bar chart is a graphical summary in which each category in a data set is represented by a rectangle whose length is proportional to the frequency, count, or summary value associated with that category. The bars are drawn with uniform width and separated by visible gaps, which signals to the reader that the horizontal axis is categorical rather than continuous.
Bar charts handle the kind of data that resists smooth measurement — counts of complaints by department, votes by candidate, defects by production line. They sit alongside the pie chart and the dot plot as the workhorses for displaying nominal or ordinal information, and they remain the most readable choice when categories number more than a handful or when precise comparison between categories matters.
Why it matters
How it works
To construct a bar chart, count or otherwise summarise the value for each category, choose a scale, and draw a rectangle for each category whose length matches that value. Categories run along one axis with consistent gaps between bars; the measured quantity runs along the perpendicular axis on a numeric scale. Bars may be vertical or horizontal — horizontal layouts work better when category labels are long or when there are many categories to fit on a screen.
The chart is read by comparing bar lengths. Sorting bars by magnitude rather than by alphabetical order usually makes the dominant categories more obvious. When the goal is composition (how a whole splits into parts), a stacked bar shows each category as a single bar segmented by sub-category. When the goal is comparison across two grouping variables, a grouped bar places multiple bars side by side per category. The right variant depends on the question the reader needs to answer, not on the data.