Measure from zero
Use centimetre intervals to measure, compare and draw line segments.
More
Offline pages
Saved on this device only. Connect at least once every 30 days to confirm Premium. Sign-out or a change of account removes saved copies.
On this page
You stopped at:
ContinueRevision Mode is on. Questions and activities are hidden.
A centimetre is a unit of length
Look at a ruler. The gap from 0 to 1 is one centimetre. We write cm. The gap from 1 to 2 is also one centimetre.
The abbreviation stays cm for one centimetre or several centimetres. We write eight centimetres as 8 cm, with a space before the unit.
Check your understanding 1 A short way to write centimetres
Choose the abbreviation to put after 8 when you mean eight centimetres.
Show answer
8 cm means eight centimetres. The number says how many; cm says which unit.
Measure a pencil by lining up one end with the zero mark, not with the edge of the ruler. Keep the ruler straight beside the pencil. Read the mark at the other end.
A pencil from 0 to 8 is 8 cm long. You count eight gaps. There are nine marks from 0 to 8, so counting the marks gives the wrong length.
The start can move
A line begins at the 2 cm mark and ends at the 7 cm mark. Its length is 5 cm, not 7 cm. Count the gaps: 2 to 3, 3 to 4, 4 to 5, 5 to 6, 6 to 7.
You can check by subtracting: 7-2 = 5.
The strip spans five centimetre gaps, even though its right end is at 7. This screen diagram is not a real-size ruler.
Check your understanding 2 A line starts away from zero
One end is at 3 cm and the other at 9 cm. How long is the line?
Show answer
6 cm. The first three centimetres of the ruler are before the line starts.
Compare lengths using the same unit
A red ribbon is 12 cm long, a blue ribbon is 9 cm long and a green ribbon is 15 cm long. From shortest to longest: blue, red, green. From longest to shortest, reverse that order: green, red, blue.
A ribbon does not become longer when you slide it along the table. Put the ends together before comparing directly.
Check your understanding 3 Two lengths are equal
Ribbon A is 6 cm long, ribbon B is 9 cm long and ribbon C is 6 cm long. Name or point to them from shortest to longest. Can A and C change places?
Show answer
A, C, B and C, A, B are both correct. A and C are equally long: each is 6 cm. B is longer at 9 cm. In an order, use every ribbon once; equal lengths may change places.
Draw and check
On paper, mark a dot at 0 and another at 6 on your ruler. Hold the ruler still and join the dots with a straight line. Measure your line again: it should be 6 cm long.
If a paper strip ends between marks, read the nearest centimetre mark. An end closer to 7 than to 8 gives 7 cm to the nearest centimetre. A screen picture is not a reliable physical centimetre: use a real ruler and paper for this action.
Check your understanding 4 Read a shifted ruler
A strip starts at 4 cm and ends at 11 cm. Sam says it is 11 cm long. Explain the mistake and find the length.
Show answer
Sam read the end mark without removing the part before the strip. The length is 11-4 = 7 cm. Sliding the strip to start at zero would put its other end at 7 cm.
Your paper measurement and drawing need a person to check them. Entering a number here does not check how you held the ruler.
Keep track of this lesson
Mark the lesson done when you have worked through it.
Lesson progress is optional and kept on this device.
Loading lesson controls…
Your lesson mark records your own study. Checks are kept separately in My Learning.