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Interpreting and creating bar graphs

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Interpreting and Creating Bar Graphs

This lesson shows how to read bar graphs that use a scale of more than one unit per line and how to compare many categories at once. It also walks through turning a table of numbers into a neat, correctly labeled bar graph of your own.

What Is a Bar Graph?

A bar graph uses rectangles, called bars, to show and compare amounts. Each bar stands for one category, like a type of pet or a day of the week. The taller or longer the bar, the bigger the amount it shows. Every bar graph needs a title, a list of categories, and a number scale so you know what each bar means.

Not every bar graph counts by ones. Many graphs use a scale, where each line on the number side stands for more than one unit, like 2, 5, or 10. Before you read any bar, check the scale first. If each line stands for 5, then a bar that reaches the second line means 10, not 2.

0 5 10 15 20 Dog Cat Fish Bird Hamster Number of Votes
Each line stands for 5 votes, so the dog bar shows 10 votes and the cat bar shows 15 votes.

In this graph, the cat bar is the tallest, so cat got the most votes. The bird bar is the shortest, so bird got the fewest votes. Because the scale counts by 5, you always multiply the number of lines a bar reaches by 5 to find its value.

Some bar graphs show four, five, or even more categories side by side. To compare them, look at each bar one at a time and write down its value. Then you can put the amounts in order from greatest to least, or find the difference between two bars by subtracting. In the pet graph above, the cat bar shows 15 and the fish bar shows 5, so 10 more people chose cat than fish.

Sometimes you start with a table of numbers instead of a finished graph. Here is a data set showing how many minutes four friends read one evening:

NameMinutes Read
Mia20
Sam35
Ella15
Tom30

To turn this table into a bar graph, follow these steps:

  1. Write the names along the bottom of the graph. These are your categories.
  2. Look at your biggest number, 35, and pick a scale that fits it well, such as counting by 5.
  3. Draw the number lines up the side, evenly spaced, using your chosen scale.
  4. Draw one bar for each friend, making every bar the same width.
  5. Stop each bar at the height that matches that friend's number of minutes.
  6. Add a title, like "Minutes Spent Reading," and label both sides of the graph.
0 10 20 30 40 Mia Sam Ella Tom Minutes Read
Each bar rises to match the number of minutes from the data table.

Before you say your bar graph is finished, check these things:

  • Does every bar start at 0 on the number side? Bars that do not start at 0 can trick people into thinking amounts are more different than they really are.
  • Are all the bars the same width, with even spaces between them?
  • Does your scale count by equal steps, like 5, 5, 5, 5, and not by mixed-up amounts?
  • Does your graph have a title and labels so someone else could understand it without asking you?

Once you can read a scaled bar graph with several categories and build one from your own numbers, you have the two biggest bar graph skills covered. From here you can move on to reading and drawing bar graphs on the wider reading and drawing bar graphs lesson, which also covers stacked bar graphs.

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