Concept 3 of 3
Bar Graphs: Bars Tell Numbers
Today's big idea
Bar height only becomes a number once you read what one step of the side scale is worth.
Two bars can be compared by eye, but their values wait on the side scale.
How it works
👀 What's going on?
Your class votes for a trip and the results go up on the board as coloured bars. From the back row you can already see which bar won. Spotting the winner takes a second, but saying by how much is the tricky half.
💡 Here's the trick
Look at the graph above. Colours run along the bottom and counts run up the side. Blue climbs to 18 while Green stops at 9, so Blue is worth exactly twice Green. Height carries the whole message.
🪄 How to do it
- 1.Check the scale up the side of the graph above and see what one step is worth.
- 2.Find the bar you want and look straight at its top edge.
- 3.Slide across to the side scale and read the number level with it.
✍️ Try it
A goals graph has a side scale that climbs in 2s. The Tigers bar stops on the third line above zero. How many goals is that? The Lions bar sits two lines higher than the Tigers bar. How many goals did the Lions score?
Three lines of 2 make 2 + 2 + 2 = 6 goals for the Tigers. Two more lines add 2 + 2 = 4 goals. So the Lions sit on 6 + 4 = 10 goals.
⚠️ Watch out
You might be thinking a bar three lines up must be worth 3. This scale climbs in 2s, so those three lines are 6, even though you counted to 3. Count the numbers printed up the side, never the lines themselves. On a scale of 5s the very same bar would read 15.
🌟 Why this matters
Weather apps, election results and a shop's busiest hours all arrive drawn as bars. One glance hands you the winner, and a second glance hands you the actual amount. Reading the scale is what turns tall and short into real numbers you can use.
Exam tip: Bars are usually drawn on a scale of 2 or 5, so read the side before you read the bar.
Watch me solve one
Quanta solves it
“Watch how I think through one of these — then you try.”
THE PROBLEM
“Bar graph shows: Red=12, Blue=18, Green=9. What is the difference between the tallest and shortest bars?”
- 1
Spot the tallest
Blue is highest at 18. 📊
- 2
Spot the shortest
Green is lowest at 9.
- 3
Subtract
18 − 9 = 9
- 4
Answer ✓
Difference = 9
Now you try one — same steps, different story 👇
See it in action
⚡ Time to play!
Slide the reader line to the top of the Tue bar to read its value.
BAR GRAPH · ROUND 1 OF 3
Quick check
✅ VERIFICATION
A bar graph has three bars. Two of them read 14 and 11, and all three together total 40. What does the third bar read?
⚡ Finish the activity above first to answer.
Keep going!