Measuring length (age 6+)
Measure the length of an object using same-size length units laid end to end with no gaps or overlaps
What a learner can do afterwards
- Measure a book by laying paper clips end to end and counting them
- Understand that the length measurement is the number of units that span the object
- Avoid gaps and overlaps when placing units
1 · Read
You already know how to tell which of two things is longer. To measure exactly how long something is, use small units that are all the same size, like paper clips or blocks. Lay them in a straight line, end to end, so they touch but do not overlap or leave gaps.
Sam measures his book by lining up 8 identical blocks along its edge, end to end, with no gaps. He counts them one by one: 1, 2, 3, 4, 5, 6, 7, 8. The book is 8 blocks long. Gaps would leave some length with no block, so the count would be too small. Overlaps would cover some length twice, so the count would be too big.
If you leave a gap between blocks, some length never gets counted, so your count is too small. If your blocks overlap, you use more of them than you need, so your count is too big.
Line up same-size units end to end, with no gaps or overlaps, then count them. That count is the length.
More to read
Measuring lengths with different units
Different units fit different things. Small lengths use centimetres. Longer walks use metres. Tiny spoons use millilitres.
Try measuring your desk. Line up the ruler at zero and read the number at the end. Write the unit too, like 30 cm.
11.1: Introducing Double Number Line Diagrams
A number line shows order. Numbers grow to the right. Jumps show adding or taking away.
Use it for sums within 100. Start at the first number, jump forward to add. Land on the answer and check with blocks.
Perimeter review
Perimeter is the walk around a shape. Add every side to find it. Squares have four equal sides.
Trace the edge with your finger. Add as you go. The total tells how much fence the shape needs.
Using Pictures to Explain Number Comparisons
Pictures help compare numbers. Longer bars mean larger amounts. Shorter bars mean smaller amounts.
Line up two bars at the start. The one that sticks out further is greater. Write it with greater than or less than signs.
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2 · Watch
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Where it sits
Learn first
Optional connections
This opens up
Where this leads
18 questions wait behind this lesson, each with its answer explained. Every answer feeds the sky: stars light as they are learned, and dim when it is time to come back.