You can measure length with things that are all the same size, like paper clips. Lay them in a straight line, end to end, starting exactly at one end of the object. Leave no gaps and no overlaps. Then count how many units fit from one end of the object to the other. Only count the units beside the object, not any that stick out past it. If the units have gaps, the object is really longer than the count; if they overlap, it is really shorter.
Explore this idea with maths tools
Maths you can move
Build 8 + 5
Tap two gold counters to fill the ten-frame.
8 in the frame + 5 waiting. The total stays the same.
Words to know
- unit
- one of the equal-sized things you measure with
- end to end
- each unit touching the next, with no gaps or overlaps
Worked examples
A pencil has 6 paper clips laid end to end beside it, from one end to the other. How many clips long is the pencil?
- 1.The clips start at one end of the pencil and stop at the other.
- 2.Count them: 1, 2, 3, 4, 5, 6.
= 6
A row of 9 clips starts 2 clips before a ribbon and ends 1 clip after it. How many clips long is the ribbon?
- 1.Leave out the 2 clips before the ribbon and the 1 clip after it.
- 2.9 − 2 − 1 = 6 clips are beside the ribbon.
= 6
Mia left gaps between her clips and counted 5. Is the straw more than, fewer than or exactly 5 clips long?
- 1.The gaps are parts of the straw with no clip on them.
- 2.Filling the gaps would need extra clips.
= more
For parents
Method: End to end, no gaps
What to say: Where does the object start and finish? Are the clips touching with no gaps?
Common mistakes:
- Counts every clip in the row, including clips that go past the end of the object.
- Starts counting at the first clip in the row even though the object starts further along.
- Counts the lines where clips start and finish instead of the clips, giving one too many.
- Counts the places where clips touch each other, giving one too few.
- Believes the count is right even when the units were laid with gaps or overlaps.
- Knows gaps or overlaps spoil the count but gets the effect backwards.