A bar chart displays data as rectangular bars. The height (or length) of each bar represents the frequency or value for that category. To read a bar chart: identify the category, read across to the y-axis scale, and note the value.
Example 1 — Read the bar chart: How many students chose Swimming?
Step 1
Find the "Swimming" bar on the x-axis
Step 2
Read the height of the bar across to the y-axis scale
Step 3
The bar reaches 18. Answer: 18 students
Example 2 — Which sport is the most popular? How many more students chose Football than Running?
Step 1
Most popular = tallest bar = Football (25 students)
Step 2
Difference = \(25 - 8 = \mathbf{17}\) more students chose Football than Running
Reading tip: If a bar falls between gridlines, estimate the value carefully. A bar halfway between 10 and 15 = 12 or 13 — state which it is closest to.
✓ Quick Check 1 — Reading bar charts
Question 1 of 10
Drawing Bar Charts Accurately
A well-drawn bar chart has specific features. In an exam you will lose marks for missing any of these. Follow this checklist every time you draw a bar chart.
Bar Chart Drawing Checklist:
☑ Title describing what the chart shows
☑ Labelled x-axis (categories) with axis title
☑ Labelled y-axis with scale starting at 0 and axis title with units
☑ Equal-width bars
☑ Equal gaps between bars
☑ Bars drawn accurately to the correct heights
Example 3 — Steps to draw a bar chart for: Mon=8, Tue=12, Wed=6, Thu=10, Fri=14
Step 1
Draw x-axis (days) and y-axis. Label both axes and add a title.
Step 2
Choose a scale for the y-axis: highest value = 14, so go up to 15 or 20. Mark equal intervals (e.g. 0, 2, 4, 6, 8, 10, 12, 14).
Step 3
Draw bars of equal width with equal gaps. Heights: Mon=8, Tue=12, Wed=6, Thu=10, Fri=14.
Step 4
Check all bars are accurate — read each height back from the chart to verify.
Common mistakes: (1) Scale not starting at 0. (2) Unequal bar widths. (3) Missing axis labels or title. (4) Bars touching with no gaps.
✓ Quick Check 2 — Drawing bar charts accurately
Question 1 of 10
Compound and Grouped Bar Charts
A compound bar chart (also called a grouped bar chart) places two or more bars side by side for each category. This makes it easy to compare two groups across multiple categories. A key (legend) is essential to identify which bar represents which group.
Example 4 — Read the grouped bar chart: Did sales increase from 2023 to 2024 in every quarter?
Step 1
In each pair of bars, compare the blue (2023) to the yellow (2024)
Step 2
In every quarter (Q1, Q2, Q3, Q4) the yellow bar (2024) is taller than the blue bar (2023)
Step 3
Yes — sales increased in every quarter from 2023 to 2024
Example 5 — Which quarter showed the greatest increase in sales?
Step 1
Estimate the difference for each quarter: Q1 ≈ 5, Q2 ≈ 15, Q3 ≈ 5, Q4 ≈ 5
Step 2
Q2 shows the largest difference between the 2023 and 2024 bars
Step 3
Q2 had the greatest increase in sales
Exam tip: A grouped bar chart question will often ask you to compare two groups. Always state the specific values you read from the chart and say which is higher/lower by how much.
✓ Quick Check 3 — Compound and grouped bar charts
Question 1 of 10
Practice
Work out each answer, then type it in and click Check to see if you're right.
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Question
Your answer
Result
1
A bar chart shows: Monday = 15, Tuesday = 12, Wednesday = 18, Thursday = 9, Friday = 15. Which day has the highest value?
2
Using the same chart, what is the value for Thursday?
3
What is the total of all five days' values?
4
What is the difference between the highest and lowest values?
5
Which day has the lowest value?
6
How many days have a value of 15 or more?
7
What is the mean (average) of all five days? (Total ÷ 5)
⚠ Things to Watch Out For
Using the wrong scale value: Always check the scale on the y-axis carefully. If 5 squares = 20, then each square = 4. Read grid lines, not midpoints between them.
Bars touching in a bar chart: Bars in a standard bar chart have GAPS between them (for categorical data). Bars only touch in frequency diagrams (grouped continuous data).
Not labelling axes: Both axes must be labelled with the quantity AND units. Missing labels lose marks.
Compound bar chart — reading total vs individual: In a compound (stacked) bar chart, read individual sections, not just the total bar height, when asked about specific categories.
Drawing bars the wrong width: All bars must be the same width. Varying bar widths suggest different amounts of data and are misleading.