Axis Title

An axis title is the short text label placed alongside a chart axis that tells the reader what the axis measures and, ideally, the units it is measured in.

Tick labels alone give you numbers, but numbers without context are ambiguous. A vertical axis reading 0, 20, 40, 60 could mean dollars, kilograms, percentages or anything else. The axis title resolves that ambiguity: a word or short phrase such as "Revenue ($ thousands)" or "Temperature (°C)" sitting next to the line. It is the difference between a chart you can interpret and a chart you have to guess at.

How an axis title appears in a chart

The horizontal axis title usually sits centered below its tick labels, written normally left to right. The vertical axis title is typically rotated 90 degrees so it runs up the left edge, parallel to the line it describes. Good titles are concise and always state units where they exist, because the same value of "5" means very different things in seconds versus hours. A title is distinct from the chart's overall title, which describes the whole figure rather than one axis.

A concrete example

Imagine a line chart of weekly website visits. The horizontal axis carries the title "Week" with tick labels Week 1 through Week 8. The vertical axis carries the title "Visits (thousands)" with ticks at 0, 10, 20, 30. A point plotted at height 30 now unambiguously reads as 30,000 visits in that week — the title supplies the "thousands," the tick supplies the "30." Remove the titles and the same point is just a dot at height 30 of something unknown.

Related terms

An axis title labels the whole axis, while individual values are marked by tick marks and their numbers. The scale determines how those values are spaced. See axis titles used well in the line chart guide.