Chapter 6: Measuring Length

How tall are you? How far is the bus stop? Length tells us "how much space from here to there". Let's measure!

What we'll learn

• Use units like centimetre, metre and kilometre.
• Pick the right unit for the right job.
• Convert between metres and centimetres.
• Estimate lengths before measuring.

The big idea

To measure length, we need a unit. Long ago, people used their hands, feet and arms. But your hand and mine are different sizes! So today we use units that are the same everywhere: centimetre (cm), metre (m), and kilometre (km).

1 metre = 100 centimetres. So a 1 m stick is the same as a 100 cm stick.

1 kilometre = 1000 metres. So a 1 km walk equals 1000 m of walking.

Use centimetres for small things (a pencil, your finger). Use metres for medium things (your height, a room). Use kilometres for long distances (between two villages).

Estimating first is a smart habit. Before measuring your eraser, guess: "about 4 cm". Then measure and check. Slowly, your guesses will get sharper.

When using a ruler, line up the 0 mark, not the end of the ruler, with the start of the object. The number where the object ends is its length.

Explore with examples

1. Convert 3 m into centimetres.

1 m = 100 cm. So 3 m = 3 × 100 = 300 cm.

2. Convert 250 cm into metres.

250 ÷ 100 = 2 m 50 cm.

3. The school field is 75 m long. Asha walks across it 4 times. How far did she walk?

75 × 4 = 300 m.

4. Which is longer: 1 km or 950 m?

1 km = 1000 m, and 1000 > 950. So 1 km is longer.

Hands-on activities

Footstep Walk

Walk across your room heel to toe. Count the steps. Note the number. Ask a family member to do the same. Whose count is more? Why?

Ruler and Riddle

Use a 30 cm ruler. Measure: a pencil, your finger, a notebook's longer side, a comb. Write down each length. Order them from shortest to longest.

Map the House

Use a measuring tape (or thread + ruler) to measure the length and width of your room. Add the four sides to find the total distance around the room , its perimeter.

Try it yourself

1. Convert 5 m to cm.
2. Convert 700 cm to m.
3. A road is 4 km long. How many metres is that?
4. Which unit fits best for measuring a sari: cm, m, or km?
5. Your pencil is 12 cm and your friend's is 9 cm. Whose is longer and by how much?
6. Mom walked 2 km, then another 850 m. Total in metres?
7. Estimate the length of a chair before measuring , then measure it.

Recap

• Standard length units: cm, m, km , small to large.
• 1 m = 100 cm, 1 km = 1000 m.
• Pick the unit that suits the object.
• Always line up the 0 mark of your ruler.