Vacation with My Nani Maa | Maths Grade 3 CBSE

Play with it

Six ideas about length

Measuring with hands and steps, then with rulers and tape. Tap each term to see what it means, with an example you can try around the house.

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Long ago, people measured with their body — hand-spans, footsteps and arm-lengths.
These are easy but not fair: a child's hand-span is smaller than Nani's, so they count differently.
Measuring the same mat, smaller hands give a bigger number of spans. The mat did not change — the unit did.

Worked example. Nani gets 6 hand-spans for a mat; you get 8. Did the mat grow?

No. Your hands are smaller, so you need more spans. The mat is the same length.

To be fair, we use standard units: the centimetre (cm) for small things and the metre (m) for big things.
100 centimetres make 1 metre. A pencil is a few cm; a door is about 2 m tall.
Use a ruler for short lengths and a measuring tape for long ones. Always start at the 0 mark.

Worked example. A crayon lines up from 0 to 7 on the ruler. How long is it?

From 0 to 7 is 7 cm. Starting at 0 makes the count correct.

To compare, measure both in the same unit, then see which number is bigger.
The difference tells how much longer or shorter — subtract the smaller from the bigger.
Estimating is a smart guess before you measure. Guess first, then check with a ruler.

Worked example. One rope is 40 cm, another is 25 cm. How much longer is the first?

40 − 25 = 15 cm longer.

Common mix-up: always start measuring from 0, not from the edge of the ruler. Starting from 1 would make every length 1 cm too long.

Where you’ll meet it

A tailor measures cloth in metres before stitching a kurta, so it is the right length.

Marking your height on a wall in centimetres shows how much you grow each year.

Before buying a mat, measure the floor so the mat fits without being too big or small.

Check yourself

Nine friendly questions to check that you can use measuring — units, rulers and comparing lengths — not just name them.

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