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CBSE Class 4 · Mathematics

Measuring Length

Official NCERT chapter from Math-Mela (book code demm1). ExamMaster notes are original teaching at CBSE Class 4 depth.

This lesson follows the official chapter “Measuring Length” in Math-Mela. The words below are ExamMaster’s teaching, not a paste from the book. Use the NCERT chapter for the classroom sequence; use these notes to hold the idea without copying exercises or figures.

  • CBSE Class 4
  • Easy level
  • 8 concepts

1Students measuring in a picture: name what is being measured

A picture of children with a scale is not a length until you name the object: desk edge, pencil, or corridor.

A scale pointing at two things at once is two measures mashed.

Figure. The first school move is to name the span. A desk has a left-to-right length; a bottle has a bottom-to-top height. Ticking the picture without naming the span answers a different question.

How it works

  1. Name the objectThis desk edge.
  2. Name the quantityLength.
  3. Point the scale at that object onlyOne object, one measure.

2A unit must repeat end to end

Spans, sticks, or centimetres must sit end to end with no gap and no overlap.

A floating unit in the middle is not a measure.

Figure. A measurement is how many of the same unit fit, each one touching the next with no gap and no overlap. Five identical pencil-widths along the rod read as 5 pencils. Mixing a pencil with a handspan mid-count is not a measurement.

How it works

  1. Pick one unitcm, or a stick.
  2. Start at one endThe object’s end.
  3. Repeat to the other endNo gaps, no overlaps.

3Start a scale at zero

The 0-mark sits at the object’s start. Starting at 1 adds a fake centimetre.

The reading is the mark at the other end, minus the start. Start at 0 and the reading is that mark.

Figure. The object on the upper scale sits from 0 to 6, so the reading is 6 cm. The same 6 cm object on the lower scale sits from 2 to 8: reading the right-hand 8 without subtracting the 2 start is the school miss. Both objects are the same length.

How it works

  1. Find 0 on the scaleThe start mark.
  2. Put 0 at the object’s endLine them up.
  3. Read the mark at the other endThat is the length.

Scale started at 1

A pencil’s tip sits on the 1 cm mark and the other end on the 12 cm mark. What length is that?

  • Start mark1 cm
  • End mark12 cm
  • Length12 − 1 = 11 cm

Pro tip. If you had started at 0, the end would have read 11 cm. Starting at 1 needs a subtract.

4Centimetres for a desk; metres for a corridor

A desk-edge is usually centimetres. A corridor is usually metres. The unit should fit the object so the number stays readable.

Measuring a corridor only in millimetres is allowed but painful.

Figure. A desk is a centimetre job; a corridor is a metre job. The two panels use different units on purpose — they are not one scale. Writing a corridor as 800 cm is legal but not the school habit; writing a desk as 0.8 m hides the centimetres you can actually see.

How it works

  1. Look at the objectDesk, or corridor.
  2. Pick a fitting unitcm, or m.
  3. Measure in that unitSay the unit after the number.

5A number without a unit is mute

“14” could be 14 cm or 14 m. Always write the unit.

Mute numbers cannot be compared.

Figure. Five is not a length. Five centimetres is. The left card is the mute number the chapter wants you to refuse; the right card is the same count with its unit attached.

How it works

  1. Finish the count14.
  2. Name the unitcm or m.
  3. Speak both14 cm, not 14.

6Estimate, then measure

Guess a nearby number in the same unit, then run the scale. The measure checks the guess.

A guess you refuse to check is stubborn, not an estimate.

Figure. Guess first, then read the scale. Here the guess is 20 cm and the scale reading is 18 cm. The estimate is allowed to be near, not exact — the point is to have a number to check the reading against.

How it works

  1. Guess in the unit you will useAbout 30 cm.
  2. MeasureScale from 0.
  3. Compare guess to measureClose, or far.

7Convert only when two units must meet

100 cm = 1 m only when you need both units in one sentence. Do not convert for fun if one unit already answers.

Inventing a rate you did not use is a guess.

Figure. One hundred centimetres and one metre are the same span written twice. Convert only when a centimetre count must sit next to a metre count. The two bars are drawn the same length because they name one length.

How it works

  1. See if two units appearcm and m.
  2. Use 100 cm = 1 mThe school rate.
  3. Rewrite only then30 cm = 0.30 m if you need metres.

8A tick on the wrong object is a different quantity

A scale along the desk height is height, not the desk’s length. The tick names whichever stretch you aligned.

Do not copy a neighbour’s number onto a different edge.

Figure. The same desk has a length along the top and a height down the side. A tick on the height does not answer a length question. Two brackets on one object are two quantities.

How it works

  1. Name the stretchThis edge.
  2. Align the scale to that stretch onlyNot the height.
  3. Read that tickA different edge needs a new read.
Starting a scale at 1 instead of 0
  1. Adds a fake centimetre unless you subtract the start
  2. Makes no difference
  3. Changes the unit to metres

0 sits at the object’s start.

Notes

  • The official chapter title is “Measuring Length”. Teach the school test for that title, not a contest shortcut.
  • If a step needs a later class, stop. The next official chapter will pick it up.

Formulas

  • Length = end-mark - start-mark (start at 0 and the length is the end-mark).
  • 100 cm = 1 m.
  • Write number + unit.

Recap

Hold these pegs from the official chapter “Measuring Length”. The wording is ExamMaster’s teaching, not a textbook recap.

Students measuring in a picture: name what is being measured
A picture of children with a scale is not a length until you name the object: desk edge, pencil, or corridor.
A unit must repeat end to end
Spans, sticks, or centimetres must sit end to end with no gap and no overlap.
Start a scale at zero
The 0-mark sits at the object’s start. Starting at 1 adds a fake centimetre.
Centimetres for a desk; metres for a corridor
A desk-edge is usually centimetres. A corridor is usually metres. The unit should fit the object so the number stays readable.
A number without a unit is mute
“14” could be 14 cm or 14 m. Always write the unit.
Estimate, then measure
Guess a nearby number in the same unit, then run the scale.

Practise Measuring Length

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  • A 4-question practice set that ends the chapter
  • 1 quick check with worked explanations
  • Timed mocks scored with the real marking scheme
  • Readiness tracked per topic, kept on your device
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