A bar chart, bar chart or column chart is a way of graphically representing a set of data or values ​​using rectangular bars of length proportional to the values ​​represented. Bar graphs can be used to compare quantities of a variable at different times or different variables at the same time. The bars can be oriented horizontally and vertically.

There is evidence of the use of this type of diagrams for more than 300 years.[1]​.

The bar graph is a way to summarize a set of data by qualitative variable categories and their frequency of appearance in a sample. It is the most common graph, reaching a percentage close to 50% in the analyzed Primary Education textbooks in Spain.[2]​.

In the bar diagram, the data are represented with rectangles with the same base on the category axis (x or abscissa axis); while the length of the other side corresponds to the value of the data, according to the scale used on the value axis (y or ordinate axis). When more than one category is represented, there are different types of presentation.

There are no strict rules applicable to bar charts, but general presentation rules are usually the following:[3]​.

This diagram is based on the results of the European Parliament Election in 2004 and 1999. The table below lists the number of seats allocated to each party. The 1999 results have been multiplied by 116,933, to compensate for the other years in between.

A bar graph representing previous results from the 2004 election would look like this:

(If all the data were arranged in descending order, this type of bar graph would be called a Pareto chart.)

This bar graph shows both results (2004 and 1999):

Currently, as technologies advance and as people use technology more, the future of the bar chart will be used more on computers, except for schools that can also change thanks to technologies.