Measuring length — Mathematics, 4–6 years
Compare how long things are, then measure a length by repeating the same-sized unit. Mathematics, 4–6 years.
How long is it?
Length tells us how far it is from one end of something to the other. We can compare objects by putting their ends together. To measure, we cover the length with equal units and count how many units fit.
Why measure
Saying that one object is longer is useful, but it does not tell everyone how long it is. People needed shared ways to make clothes, build houses and fit objects together. Using equal units makes a measurement that others can check.
Measure with cubes
Place cubes in a straight line beside a pencil, with no gaps and no overlaps. Count them: one, two, three, four. The pencil is four cubes long. If the cubes are moved apart, they still count as four cubes, but they no longer show the pencil’s length.
The gap trap
A common mistake is to leave gaps between the measuring objects, or to start beside the object instead of at its end. It feels reasonable because the objects are still in a row. Begin exactly at one end, keep them touching, and finish exactly at the other end.
Measuring in life
You measure when checking whether a toy fits on a shelf, comparing ribbons or deciding how much paper is needed. A ruler uses standard units, while blocks or hand spans are useful for rough comparisons. Different units can give different numbers for the same object.
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