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Bar graphs

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How to Make a Bar Graph

This topic teaches the basics of bar graphs: what their parts are, how to read bar heights against a scale, and how to build a bar graph from a set of collected data. It includes a fully worked example with a labeled diagram and simple comparison questions to practice reading bars accurately.

What Is a Bar Graph?

A bar graph (also called a bar chart) is a way of showing information using rectangular bars. Each bar's length or height shows the value of a category, so you can compare different groups at a glance. Bar graphs are one of the simplest ways to display data once it has been organized, which is why they usually come right after you learn about collecting data.

Bar graphs are closely related to pictographs, since both compare categories using pictures or shapes instead of raw numbers. The difference is that a bar graph uses bars measured against a scale, while a pictograph uses repeated symbols.

Every bar graph has the same basic parts, no matter what data it shows:

  • Title: tells you what the graph is about.
  • Axes: one axis lists the categories (such as types of fruit), and the other axis shows a numeric scale (such as number of votes).
  • Scale: the evenly spaced numbers along the numeric axis that let you measure each bar.
  • Bars: rectangles whose height (or length) shows the value for each category.

Bars in a basic bar graph are always the same width and evenly spaced. Only the height changes, since that is what represents the value.

To read a bar graph, look at where the top of a bar lines up with the numeric scale. That number is the value for that category. The example below shows how many students picked each fruit as their favorite.

Favorite Fruit 0 2 4 6 8 Apple Banana Orange Grape Fruit
Bar graph of favorite fruit votes among a class.

Looking at the graph, the banana bar reaches 8, so 8 students chose banana. The orange bar reaches 3, so only 3 students chose orange. Comparing bars this way, we can say banana got the most votes and orange got the fewest. Building sentences like these is exactly the skill covered in comparative language, which pairs naturally with bar graphs.

Once your data is collected and organized into categories with counts, follow these steps:

  1. Draw the axes. One axis lists the categories, the other will hold the numeric scale.
  2. Choose a scale. Look at the largest value in your data and pick evenly spaced numbers that reach at least that high. In the fruit example, the scale counts by 2s up to 8, since the largest value is 8.
  3. Label the categories evenly along the category axis, leaving equal space for each bar.
  4. Draw each bar so its height matches the correct value on the scale. Keep every bar the same width.
  5. Add a title that describes what the graph shows, and label both axes clearly.

For example, suppose a survey of pets owned by a class gives: dogs 6, cats 4, fish 2, birds 1. The largest value is 6, so a scale counting by 1s or 2s up to 6 works well. You would then draw four bars of equal width, one for each pet, with heights of 6, 4, 2, and 1.

Using the fruit bar graph above, try answering these on your own before checking the values in the graph:

  • Which fruit was the most popular?
  • How many more students chose banana than apple?
  • How many students voted in total?

To check your answers: banana was the most popular with 8 votes, banana had 3 more votes than apple ( \(8 - 5 = 3\) ), and the total number of votes is \(5 + 8 + 3 + 6 = 22\).

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