Chapter 0 of 14

CBSE Class 3 Mathematics★ 4–5 marks · CBSE Class 3 Mathematics (Math-Magic) Chapter 4

Long and Short

Measurement of length — centimetres, metres, kilometres. Estimating and comparing lengths. Standard units and tools. CBSE Class 3 Mathematics (Math-Magic) Chapter 4.

⏱ 8 min readEasy difficulty✓ Free · NCERT-aligned

Ask AI about this

🔤Build your vocabulary from this chapterLexiGenome mines the key words, explains them in your language, and schedules them with spaced repetition.Mine words →

By the end of this chapter you'll be able to…

1Identify standard units of length: centimetre (cm) for short objects, metre (m) for medium, kilometre (km) for long distances
2Estimate lengths using benchmarks: little finger width ≈ 1 cm, a door height ≈ 2 m, walking distance between landmarks ≈ 1 km
3Compare lengths — which is longer/shorter, taller/shorter, and by how much
4Convert between cm and m (100 cm = 1 m) and between m and km (1000 m = 1 km)
5Use a ruler/scale correctly to measure in centimetres

💡

Why this chapter matters

Measurement is one of the most practical math skills — children use it every day without realizing. This chapter introduces standard units of length (centimetre, metre, kilometre), teaches estimation (about how long?), and provides real-world benchmarks (little finger ≈ 1 cm, a door ≈ 2 m). It bridges the gap between informal 'this is longer than that' and formal measurement, a key step in mathematical thinking.

Before you start — revise these

A 5-minute refresher here will save you 30 minutes of confusion below.

🔗

Class 2 Mathematics: Long and Short (basic comparison)

Must understand the concept of longer/shorter, taller/shorter from Class 2 — now adding standard units.

Long and Short

What is Length?

LENGTH tells us HOW LONG something is. It also tells us how TALL or how FAR.

The length of a PENCIL
The height of a DOOR
The distance from HOME to SCHOOL

We use DIFFERENT units to measure different lengths.

Units of Length

Centimetre (cm)

A CENTIMETRE is a SMALL unit. We use it for SHORT things.

Thing to Measure	Approximate Length
Your little finger	About 1 cm wide
A pencil	About 15-20 cm
An eraser	About 3-5 cm
A book	About 20-30 cm
A mobile phone	About 12-15 cm

1 cm is about the WIDTH of your little finger!

Metre (m)

A METRE is a BIGGER unit. We use it for MEDIUM things.

Thing to Measure	Approximate Length
A door	About 2 m tall
A classroom	About 6-8 m long
A car	About 4 m long
A bed	About 2 m long
A skipping rope	About 2-3 m

1 metre = 100 centimetres

A metre stick has 100 small marks — each mark is 1 cm.

Kilometre (km)

A KILOMETRE is a VERY BIG unit. We use it for LONG distances.

Thing to Measure	Approximate Distance
Walk to school	1-2 km
From your home to the market	2-5 km
Between two cities	50-500 km
A marathon race	About 42 km

1 kilometre = 1000 metres

Measuring Tools

Tool	Used For
Ruler	Measuring small things in cm
Measuring tape	Measuring curved things (like your waist)
Metre stick	Measuring medium lengths in m
Odometer	Measuring distance travelled by a vehicle

How to Measure with a Ruler

Step-by-Step

Place the ruler along the object you want to measure
Align the 0 mark with one END of the object
See where the other end FALLS on the ruler
Read the number — that is the LENGTH

Important!

Always measure from the 0 mark, NOT from the edge of the ruler
Keep your eye LEVEL with the mark — looking from an angle gives a WRONG reading
Measure in a STRAIGHT line

Comparing Lengths

Which is Longer?

A pencil (15 cm) vs an eraser (3 cm) → Pencil is LONGER
A door (2 m) vs a book (25 cm) → Door is LONGER

Which is Shorter?

A snake (1 m) vs a worm (5 cm) → Worm is SHORTER

Putting in Order

Arrange from SHORTEST to LONGEST:

Pencil (15 cm), Eraser (3 cm), Book (25 cm), Desk (1 m = 100 cm)
Order: Eraser (3 cm) → Pencil (15 cm) → Book (25 cm) → Desk (100 cm)

Estimation of Length

ESTIMATION means making a SMART GUESS about length WITHOUT measuring.

Practice Estimating

Estimate the length of your desk: ___ cm. Now measure it. How close were you?
Estimate the height of your friend: ___ cm. Now measure. Were you close?
Estimate the width of your classroom: ___ m. Now measure with your footsteps.

Tips for Better Estimation

Remember that your LITTLE FINGER is about 1 cm wide
Remember that a DOOR is about 2 m tall
Your FOOTSTEP is about 30-40 cm (1 foot length)
Your STRIDE (one big step) is about 1 m

Converting Units

cm to m

100 cm = 1 m 200 cm = 2 m 300 cm = 3 m

To convert cm to m: Divide by 100. 450 cm = 400 cm + 50 cm = 4 m 50 cm

m to cm

1 m = 100 cm 3 m = 300 cm 7 m = 700 cm

To convert m to cm: Multiply by 100. 5 m = 5 × 100 = 500 cm

m to km

1000 m = 1 km 2000 m = 2 km

To convert m to km: Divide by 1000. 3500 m = 3000 m + 500 m = 3 km 500 m

km to m

1 km = 1000 m 5 km = 5000 m

To convert km to m: Multiply by 1000. 2 km = 2 × 1000 = 2000 m

Fun Activities

Activity 1: Measure Yourself

Your height: ___ cm
Your arm length: ___ cm
Your foot: ___ cm

Activity 2: Find Things

Find things in your home that are:

About 1 cm long (a ___ )
About 10 cm long (a ___ )
About 1 m long (a ___ )
About 10 m apart (from ___ to ___ )

Activity 3: How Many Footsteps?

Measure your classroom in FOOTSTEPS:

Length: ___ footsteps
Width: ___ footsteps
Now multiply by your foot length (about 25 cm) to get centimetres!

Common Mistakes

'A metre has 1000 centimetres.' — No! 1 metre = 100 centimetres. 1 kilometre = 1000 metres.
'I can measure the door with my ruler.' — A ruler (15-30 cm) is too SMALL for a door. Use a METRE STICK or MEASURING TAPE.
'Measuring from the 1 mark instead of 0.' — Always use the 0 mark. If you start at 1, subtract 1 from your reading.
'5 m is the same as 5 cm.' — No! 5 m = 500 cm. These are VERY different lengths.
'A long object is always heavier.' — Length and weight are DIFFERENT. A long hollow pipe is light. A short iron rod is heavy.

Quick Self-Test

Q1: How many centimetres are in 1 metre? A1: 100 centimetres.

Q2: Which unit would you use to measure the distance between two cities? A2: Kilometres (km).

Q3: Convert 5 m into cm. A3: 5 m = 500 cm.

Q4: Which is longer: 1 km or 500 m? A4: 1 km (1 km = 1000 m, which is MORE than 500 m).

Q5: A pencil is 15 cm. An eraser is 3 cm. How much longer is the pencil? A5: 15 - 3 = 12 cm longer.

Q6: How tall do you think a door is? A6: About 2 m.

Q7: Convert 450 cm into metres. A7: 450 cm = 4 m 50 cm.

Q8: Name one tool used to measure length. A8: Ruler (or measuring tape, metre stick).

Key formulas & results

Everything you need to memorise, in one card. Screenshot this for revision.

Units of length and their use

Centimetre (cm): small things — pencil (15 cm), eraser (3 cm), book (20 cm), finger width (1 cm) · Metre (m): medium things — door (2 m), car (4 m), room (5 m), person's height (~1.5 m) · Kilometre (km): long distances — school to home (2 km), city to city (100 km+)

Choose the right unit: cm for small, m for medium, km for long. Don't measure a pencil in km!

Unit conversions

1 m = 100 cm · 1 km = 1000 m · To convert m to cm: multiply by 100 (e.g., 3 m = 3 × 100 = 300 cm) · To convert km to m: multiply by 1000 (e.g., 2 km = 2 × 1000 = 2000 m) · To convert cm to m: divide by 100

At Class 3 level, focus on understanding 1 m = 100 cm and 1 km = 1000 m. Formal multiplication/division for conversions comes later.

Body-based benchmarks (for estimation)

Width of little finger ≈ 1 cm · Length of handspan ≈ 15-20 cm · Length from elbow to fingertip ≈ 30-40 cm · One big step (stride) ≈ 1 m · Height of a door ≈ 2 m · Walking 10-15 minutes ≈ 1 km

These benchmarks help children ESTIMATE without a ruler. 'About how long is this table? About 2 handspans — so roughly 40 cm.'

Comparing lengths

To find how much longer/shorter: subtract the smaller length from the larger length. Example: Pencil A = 18 cm, Pencil B = 12 cm. Pencil A is 18 − 12 = 6 cm longer than Pencil B.

Always use the SAME unit when comparing. Don't compare '2 m' with '150 cm' without converting first.

⚠️

Common mistakes & fixes

These are the exact errors that cost students marks in board exams. Read them once, save yourself the trouble.

WATCH OUT

✗ Using the wrong unit — measuring a pencil in metres or distance to school in centimetres

✓ Ask: 'Is this small, medium, or large?' Small → cm, medium → m, large → km. A pencil is small → cm. Distance to school is large → km.

WATCH OUT

✗ Confusing 100 cm = 1 m — thinking 1 m = 10 cm or 1000 cm

✓ Memorize: 1 METRE = 100 CENTIMETRES. Visual aid: a metre scale has 100 small cm marks on it. 'CENTI' means hundred — 100 centimetres make 1 metre.

WATCH OUT

✗ Starting measurement from the edge of the ruler instead of the 0 mark

✓ Always align the START of the object with the 0 mark on the ruler, not the edge of the ruler (some rulers have a gap before 0). Read where the object ENDS.

NCERT exercises (with solutions)

Every NCERT exercise from this chapter — what it covers and how many questions to expect.

Estimation and measurement

Estimate lengths, then measure with ruler; choose correct unit (cm/m/km); compare lengths

Questions

Real-world application

Distance between places; heights of family members; lengths of everyday objects

Questions

Practice problems

Try each one yourself before tapping "Show solution". Active recall > rereading.

Q1EASY· Unit Choice

Which unit would you use to measure the length of a pencil — cm, m, or km?

▶ Show solution

Centimetre (cm). A pencil is a small object, about 15 cm long. Metres are too big and kilometres are for long distances only.

Q2EASY· Conversion

How many centimetres are there in 3 metres?

▶ Show solution

3 metres = 3 × 100 = 300 centimetres. (1 m = 100 cm, so multiply by 100.)

Q3EASY· Compare

Rope A is 250 cm long. Rope B is 2 m long. Which is longer and by how much?

▶ Show solution

Convert to same unit: 2 m = 200 cm. Rope A = 250 cm, Rope B = 200 cm. Rope A is longer by 250 − 200 = 50 cm.

Q4EASY· Real-world

The distance from Anu's home to school is 2 km. How many metres is that?

▶ Show solution

2 km = 2 × 1000 = 2000 metres. Anu walks 2000 m to school every day.

Q5MEDIUM· Estimation

Estimate the height of your classroom door using body benchmarks. Then explain your estimate.

▶ Show solution

A standard door is about 2 metres tall. I know this because: (1) most adults are about 1.5-1.8 m tall, and a door is slightly taller than an adult, (2) 1 big step is about 1 m, so 2 big steps would reach the top of the door. Estimated height: about 2 m.

5-minute revision

The whole chapter, distilled. Read this the night before the exam.

•Units of length: centimetre (cm) for small objects, metre (m) for medium, kilometre (km) for long distances
•1 metre (m) = 100 centimetres (cm); 1 kilometre (km) = 1000 metres (m)
•Body benchmarks: little finger width ≈ 1 cm, one big step ≈ 1 m, 10-15 min walk ≈ 1 km
•To compare lengths, use the SAME unit. Convert if needed (e.g., 2 m = 200 cm)
•To find how much longer: subtract smaller length from larger length
•When measuring with ruler: align object start with 0 mark, read where it ends — not the ruler edge

CBSE marks blueprint

Where the marks come from in this chapter — so you can plan your prep.

Typical chapter weightage: 4–5 marks in Class 3 Mathematics assessment

Question type	Marks each	Typical count	What it tests
Fill in the blanks / MCQ (1 mark)	1	2	Choosing correct unit (cm/m/km); 1 m = ___ cm; comparing lengths from given data
Short answer (2 marks)	2	1–2	Converting between units; comparing two lengths (which is longer and by how much); estimation

Prep strategy

Give your child a ruler and let them measure 5 objects at home — pencil, book, phone, spoon, toy
Use body benchmarks daily: 'This book is about 2 handspans long — so about 30 cm?'
Walk 1 km together — count steps or time it. Discuss: 'This is what 1 km feels like.'
Create a 'Length Chart': list objects at home with estimated length and actual measured length
Play 'Longer or Shorter?': hold up two objects and guess which is longer, then measure to check

AI helpers for this chapter

Generate more practice on the fly, or have the chapter explained at a different level.

⚡

Generate 5 more questions

Fresh MCQs + short-answer items based on this chapter, plus answer keys.

🧠

Explain at a different level

Re-explain the chapter at the level you actually want.

📝 My notes

Saved on this device — sign in to sync · how this works

0/600

Practice more, ask doubts, find a tutor

CBSE Class 3 mock tests

CBSE Class 3 PYQs

Ask in Q&A

Mathematics flashcards

Related chapters

Students who read Long and Short usually read these next.

What's in a Name?

The opening chapter of CBSE Class 3 Mathematics (Maths Mela). Children collect and compare simple information (data) using their own names — counting letters, finding the longest and shortest names, sorting, and showing results in tables and picture graphs. These notes give the core ideas, worked examples, an activity, common mistakes, a practice set with answers, and quick revision.

Toy Joy

A CBSE Class 3 Mathematics (Maths Mela) chapter on solid (3D) shapes — cube, cuboid, cylinder, cone, and sphere. Using toys and everyday objects, children explore flat and curved surfaces and notice which shapes roll, slide, and stack. These notes give the core ideas, worked examples, an activity, common mistakes, a practice set with answers, and quick revision.

Double Century

A CBSE Class 3 Mathematics (Maths Mela) chapter that takes numbers beyond 100 up to 200 — a "double century". Children read, write, and compare numbers to 200, build them from hundreds, tens, and ones, estimate quantities, and spot number patterns. These notes give core ideas, worked examples, an activity, common mistakes, a practice set with answers, and quick revision.

Vacation with My Nani Maa

A CBSE Class 3 Mathematics (Maths Mela) chapter that practises addition and subtraction through a holiday with Nani Maa (grandmother). Children add and take away with two- and three-digit numbers, estimate totals, and solve real-life word problems. These notes give core ideas, worked examples, an activity, common mistakes, a practice set with answers, and quick revision.