Measuring Length in cm and m
In Class 3, you learn to measure lengths using two standard units: centimetre (cm) and metre (m). Short objects like pencils and books are measured in centimetres. Longer objects like the length of a room or a playground are measured in metres.
You use a ruler to measure in centimetres and a metre stick or measuring tape to measure in metres.
What is Measuring Length in cm and m - Class 3 Maths (Measurement)?
Centimetre (cm) is a unit for measuring short lengths. Your fingernail is about 1 cm wide.
Metre (m) is a unit for measuring longer lengths. A door is about 2 metres tall.
1 metre = 100 centimetres | 1 m = 100 cm
Measuring Length in cm and m Formula
1 m = 100 cm | 1 cm = 1/100 m
How to measure with a ruler:
- Place the 0-mark of the ruler at one end of the object.
- Read the number at the other end.
- That number is the length in cm.
Types and Properties
When to use which unit:
| Measure in cm | Measure in m |
|---|---|
| Length of a pencil (15 cm) | Length of a classroom (10 m) |
| Width of a notebook (18 cm) | Height of a door (2 m) |
| Height of a tiffin box (8 cm) | Length of a cricket pitch (22 m) |
| Length of a finger (7 cm) | Width of a road (8 m) |
Solved Examples
Example 1: Measure a Pencil
Question: Ria places a pencil along a ruler. The pencil starts at 0 cm and ends at 14 cm. How long is the pencil?
Think:
- Length = 14 − 0 = 14 cm
Answer: The pencil is 14 cm long.
Example 2: Measure Not Starting at 0
Question: A ribbon is placed on a ruler from 3 cm to 11 cm. How long is the ribbon?
Think:
- Length = 11 − 3 = 8 cm
Answer: The ribbon is 8 cm long.
Example 3: Choose the Right Unit
Question: Which unit would you use to measure the length of a school bus — cm or m?
Think:
- A school bus is very long, several metres.
- Centimetres would give a very large number.
Answer: Use metres (m).
Example 4: Estimate Length
Question: Estimate the length of your maths textbook. Then measure with a ruler.
Think:
- Estimate: about 25 cm.
- Measured: 24 cm.
Answer: The textbook is about 24 cm long. The estimate was close.
Example 5: Add Lengths
Question: Aman has two ropes — one is 45 cm and the other is 55 cm. What is the total length?
Think:
- 45 + 55 = 100 cm = 1 m
Answer: Total length = 100 cm = 1 m.
Example 6: Subtract Lengths
Question: A table is 120 cm long. A cloth on it is 85 cm long. How much of the table is uncovered?
Think:
- 120 − 85 = 35 cm
Answer: 35 cm of the table is uncovered.
Example 7: Real-life Measurement
Question: The blackboard in class is 3 m long. How many centimetres is that?
Think:
- 1 m = 100 cm
- 3 m = 3 × 100 = 300 cm
Answer: The blackboard is 300 cm long.
Example 8: Word Problem
Question: Priya is 1 m 25 cm tall. How tall is she in cm only?
Think:
- 1 m = 100 cm
- 100 + 25 = 125 cm
Answer: Priya is 125 cm tall.
Example 9: Compare Lengths
Question: Which is longer: 2 m or 150 cm?
Think:
- 2 m = 200 cm
- 200 cm > 150 cm
Answer: 2 m is longer.
Key Points to Remember
- Centimetre (cm) is used for short lengths; metre (m) is used for longer lengths.
- 1 m = 100 cm.
- Use a ruler for cm and a metre stick or tape for m.
- To measure: place the 0-mark at one end, read the other end.
- If not starting at 0, subtract the starting number from the ending number.
- Always write the unit (cm or m) with the number.
Practice Problems
- A crayon starts at 2 cm and ends at 9 cm on a ruler. How long is the crayon?
- Would you measure the height of your classroom door in cm or m?
- Dev's desk is 60 cm long. Ria's desk is 75 cm long. How much longer is Ria's desk?
- A rope is 2 m 30 cm long. Write this in cm only.
- Which is longer: 3 m or 250 cm?
- Neha's height is 130 cm. Write this in m and cm.
- A garden is 5 m long. How many centimetres is that?
Frequently Asked Questions
Q1. What is a centimetre?
A centimetre is a unit of length. It is about the width of your fingernail. 100 centimetres make 1 metre.
Q2. What is a metre?
A metre is a larger unit of length equal to 100 centimetres. It is about the length of a big step or the width of a door.
Q3. How many cm are in 1 m?
There are 100 cm in 1 m.
Q4. When should I use cm and when should I use m?
Use cm for short objects like pencils, books, and erasers. Use m for longer things like rooms, buildings, and playgrounds.
Q5. How do I measure if my ruler does not start at 0?
Place any mark at one end of the object and note the number at the other end. Subtract the smaller number from the larger to find the length.
Q6. What tool do I use to measure in metres?
Use a metre stick, a measuring tape, or a long ruler marked in metres.
Q7. How do I write 1 m 50 cm in centimetres only?
Convert metres to cm: 1 m = 100 cm. Then add: 100 + 50 = 150 cm.
Q8. Is this covered in NCERT Class 3?
Yes. NCERT Class 3 Maths covers measurement of length using cm and m, including estimation, actual measurement, and word problems.
