Comparing with bars
A bar graph uses bars to show and compare amounts. The longer the bar, the bigger the amount. Bar graphs are great for comparing categories: favourite sports, pets, colours, or sales by month.
Parts of a bar graph
| Part | Job |
|---|---|
| Title | Tells what the graph is about |
| Category axis | Lists the categories (one bar each) |
| Value axis | Shows the numbers, using a scale |
| Labels | Name each axis |
| Bars | Show the amounts; all the same width with equal gaps |
Vertical and horizontal
- In a vertical bar graph, bars go up. Categories are along the bottom.
- In a horizontal bar graph, bars go across. Categories are down the side.
Both work the same way. Horizontal bars are handy when category names are long.
Choosing a scale
The scale must go up in equal steps. Pick a step that fits your biggest value without making the graph too tall.
| Biggest value | Good step |
|---|---|
| 10 | 1 or 2 |
| 50 | 5 or 10 |
| 300 | 50 or 100 |
Start the scale at 0. Starting higher exaggerates differences and can mislead readers.
Making a bar graph
Data: Favourite season: Summer 12, Winter 8, Fall 6, Spring 4.
- Write a title: "Favourite Seasons in Grade 4".
- Draw and label the axes: "Season" and "Number of students".
- Choose a scale: 0, 2, 4, 6, 8, 10, 12.
- Draw one bar for each season, same width, with gaps between.
- Check each bar’s height matches the data.
Reading a bar graph
- Read across from the top of each bar to the scale.
- If the bar ends between two numbers, estimate. A bar halfway between 10 and 12 shows 11.
Double bar graphs
A double bar graph shows two sets of data side by side, like boys’ and girls’ favourite seasons. A key tells you which colour is which.
Worked examples
From the season data above:
Example 1: Which season is most popular?
Summer (12).
Example 2: How many more chose winter than spring?
8 − 4 = 4.
Example 3: How many students were surveyed?
12 + 8 + 6 + 4 = 30.
Common mistakes
- Uneven scales (0, 5, 10, 20, 50), which distort the picture.
- Bars of different widths.
- Forgetting the title or axis labels.
- Starting the scale above 0, which makes small differences look huge.
Try it yourself
A bar graph shows books read: Ava 7, Ben 4, Cal 9, Dee 6.
- Who read the most?
- How many books did they read altogether?
- What would be a good scale step?
- How many more did Cal read than Ben?
Answers: 1) Cal 2) 26 3) 1 or 2 4) 5
Quick recap
- A bar graph compares categories with bar lengths.
- Use a clear title, labels and an even scale starting at 0.
- Bars can be vertical or horizontal.