A map uses 1 cm : 2.5 km. What does 7.2 cm represent?
- Each centimetre represents 2.5 km.
- 7.2 × 2.5 = 18 km.
- Check: 18 ÷ 7.2 = 2.5 km per cm.
Scale drawings & maps
Shrink the representation. Preserve the relationship.
A scale compares drawing to reality
A scale of 1 : 500 means 1 unit on the drawing represents 500 of the same units in reality. For 1 cm : 5 m, converting 5 m to 500 cm gives the same scale.
See the quantities change.
Predict before changing a value. The written explanation below remains available without JavaScript.
Use the direction the question needs
To find actual length from drawing length, multiply by the actual-length-per-drawing-unit rate. To find drawing length, divide actual length by that rate. Label the two quantities before calculating.
Length and area scale differently
If every length is multiplied by 3, area is multiplied by 9. A scale factor is a length factor unless stated otherwise. Changing only one dimension distorts the shape.
Khan Academy
Pause the explanation before a calculation. Predict the next step and explain which quantities are being compared.
Worked examples
A 12 m wall is drawn at 1 : 200. How long is it on paper?
- 12 m = 1200 cm.
- Drawing length = 1200 ÷ 200 = 6 cm.
- Check: 6 cm × 200 = 1200 cm.
Try it before checking.
At 1 cm : 4 km, what does 3.5 cm represent?
A first hint
Multiply the map length by 4 km per cm.
Compare your reasoning
3.5 × 4 = 14 km.
Practise the skill.
Fresh questions · useful feedback
Build fluency, one decision at a time.
Work through eight questions. Two independent correct answers introduce a harder version; supported answers bring the next question back to the foundation. You can use hints at any time.
0 of 8 questions completed
This round saves on this device. It is practice, not a school mark.
Explain a little more.
A photo is doubled in width and height. How does its area change?
Use this thinking in the If… project →