Bar graphs

A bar graph uses rectangular bars to show data. The height (or length) of each bar shows how big the count is. Bar graphs are like pictographs, but cleaner , every bar is just a rectangle.

What is this?

A bar graph has two axes:

• The horizontal axis (along the bottom) , the categories (apples, mangoes, days of the week, …).
• The vertical axis (going up) , the scale of counts (0, 5, 10, 15, 20, …).

Each bar stands on a category and goes up to the count. Taller bar = bigger count.

To draw a bar graph:

1. Draw the two axes on grid paper.
2. Mark the categories along the horizontal axis, evenly spaced.
3. Choose a scale for the vertical axis (e.g., each square = 5 votes). The scale must fit the biggest data point.
4. For each category, draw a bar up to its count. Use equal bar widths and equal spacing.
5. Colour the bars and label both axes.

The bars must all start from the same baseline (the horizontal axis) so we can compare heights fairly.

Reading a bar graph is easy:

• The tallest bar shows the most popular category.
• The shortest bar shows the least.
• To find the count for a bar, look at the vertical axis at the top of that bar.

Bar graphs are used everywhere , election results, cricket scores, weather charts, news headlines about populations or prices.

Worked examples

Example 1. Children's marks in a test: Asha 35, Babu 40, Chitra 30, Dev 45. Draw a bar graph with scale 1 square = 5 marks.

• Asha: bar height 7 squares (35 ÷ 5).
• Babu: 8 squares.
• Chitra: 6 squares.
• Dev: 9 squares.

Example 2. From a bar graph, the rainfall in 4 months was June 80 mm, July 120 mm, Aug 100 mm, Sep 60 mm. Which month had the most rain?

• July , tallest bar (120 mm).

Example 3. A bar shows "books read" with bar height of 8 units. If scale is 1 unit = 3 books, how many books were read?

• 8 × 3 = 24 books.

Try it

1. Make a bar graph for: Cricket 12, Football 8, Hockey 6, Tennis 4. Choose your own scale.
2. From a bar graph, the bar for one fruit is 6 cm tall. If scale is 1 cm = 5 fruits, how many fruits?
3. A bar graph shows attendance Mon to Fri: 25, 30, 28, 26, 30. Which days had highest attendance?
4. How is a bar graph different from a pictograph?
5. Use the data , Wheat 50 kg, Rice 35 kg, Dal 20 kg, Sugar 15 kg , to draw a bar graph.

Hands-on

Class scores. Get the maths test marks of 5 friends. Draw a bar graph on square paper. Use a scale that fits the highest mark.

Weekly weather. For one week, note the day's temperature at noon. Draw a bar graph at the end of the week with day on the horizontal axis and temperature on the vertical axis.