A bar chart is just rectangles standing up next to each other. Each bar represents one category — a month, a day, a class, a colour — and its height tells you the value. In Year 4 the values get big, so the scale on the side stops counting by 1s and starts counting by 5s, 10s, 50s or even 100s.
The scale comes first
Before you read a single bar, read the scale.
If the vertical axis is labelled 0, 10, 20, 30, 40, 50, … each gridline up is 10 units.
If the axis is 0, 5, 10, 15, 20, … each gridline up is 5 units.
If the axis is 0, 100, 200, 300, … each gridline up is 100 units.
To find a bar's value, slide your finger along the top of the bar to the scale on the left and read off the number where it lands.
When a bar ends between two gridlines
Most bars don't end exactly on a gridline. Look at the distance the bar overshoots the lower gridline:
Scale steps of 10. A bar reaches halfway between 30 and 40. Value = 35.
Scale steps of 5. A bar reaches one-fifth of the way past 20. Value = 20 + 1 = 21.
If the bar lands clearly between two gridlines but you can't tell exactly where, round to the nearest gridline value. The chart's job is to show "about how much", not always to the unit.
A worked example
A library counted books borrowed in five months:
| Month | Books |
|---|---|
| January | 80 |
| February | 60 |
| March | 110 |
| April | 90 |
| May | 130 |
Drawn as a bar chart with vertical scale 0, 10, 20, …, 140.
Read off:
- January bar reaches 80 (between 70 and 90, on the 80 gridline).
- May bar reaches 130 (between 120 and 140).
Now answer:
Q. How many more books were borrowed in May than in February?
130 − 60 = 70 books.
Q. Which month had fewer books than April?
April has 90. Bars shorter than April: January (80) and February (60). So two months.
Q. What was the total for the five months?
80 + 60 + 110 + 90 + 130 = 470 books.