Dual Bar and Compound Bar Charts
Dual bar charts place two bars side by side for each category so you can compare two data sets. Compound (stacked) bar charts stack the bars on top of each other to show totals.
A dual bar chart (also called a comparative bar chart) draws two bars next to each other for every category — one for each data set. This makes it easy to compare the two groups at a glance.
A compound bar chart (also called a stacked bar chart) places the bars for each group on top of each other. The total height of each stack shows the combined frequency, while the sections show how much each group contributes.
Both types need a key (legend) so the reader knows which colour represents which group.
Use the mode selector below to switch between dual and compound views.
Watch it work
Question: Year 7 and Year 8 were asked their favourite sport. Football: Y7 = 12, Y8 = 9. Tennis: Y7 = 6, Y8 = 8. Swimming: Y7 = 10, Y8 = 11. Draw a dual bar chart.
Step 1: Set up axes — categories along the bottom, frequency up the side (0 to at least 12). Add a key for Year 7 and Year 8 with different colours.
Step 2: For each sport, draw two bars side by side. Football: Y7 bar to 12, Y8 bar to 9. Tennis: Y7 bar to 6, Y8 bar to 8. Swimming: Y7 bar to 10, Y8 bar to 11.
Step 3: Check by comparing — for example, Year 7 preferred football the most, while Year 8 preferred swimming. The dual bars make this comparison clear.
Have a go
Q1. In a dual bar chart, Group A's bar for "Red" is 8 and Group B's bar is 5. Which group has more reds?
Group A — 8 is greater than 5.
Q2. In a compound bar chart, a stack has a blue section of height 6 and a red section of height 4. What is the total frequency for that category?
Q3. When would you choose a compound bar chart over a dual bar chart?
When you want to show the total for each category as well as how each group contributes to that total.
Q4. Why is a key (legend) essential on both dual and compound bar charts?
Without a key, the reader cannot tell which colour represents which group, so the chart is meaningless.