Bar Chart

Comparing amounts across categories with lengths a reader can rank instantly.

Also known as: bar graph, column chart, bar diagram

A bar chart compares amounts across categories using length. One bar per category, one shared baseline, and the reader can rank them instantly without reading a single number.

Sessions by channel (e.g.)

paid search  ########################  1,240
organic      ####################      1,050
email        #######                     380
referral     ###                         160

Rules that make one readable

Start the value axis at zero. The length is the claim the bar makes; truncating it exaggerates every difference (see axis truncation).
One bar per category. If your horizontal axis is a continuous measure rather than a set of categories, you want a histogram.
Sort by value, unless the categories have a natural order — days of the week, age bands, plan tiers. Then keep that order, because the reader expects it.
Long labels mean horizontal bars. Rotating labels 45 degrees to fit vertical bars costs more than it saves.
Do not colour each bar differently. Colour earns its place when it carries a grouping, not when it decorates.
Label the values when the reader will quote them. Length is for ranking, not for reading.

When not to use it

Past roughly a dozen categories a bar chart becomes a wall, however well sorted. Group the tail into “other”, or switch to a Pareto chart when the question is prioritisation, or a treemap when the parts are many and belong in a hierarchy. If the composition of each bar matters, that is a stacked bar chart, with the readability cost that comes with it.