📏 Length, Weight and Capacity
Class 4 Maths · Unit 8 of 12 · about 120 minutes
This unit introduces standard units of length (km, m, cm), weight (kg, g) and capacity (L, mL). Children learn to choose the right unit, convert between units within the same system, add and subtract measures with regrouping, and estimate and measure everyday objects. The unit builds on place value and arithmetic skills from earlier units and prepares for perimeter, area and money.
What your child will learn
- Students will be able to choose the appropriate standard unit (km, m, cm; kg, g; L, mL) for measuring a given object or distance.
- Students will be able to convert between units within the same system (m to cm, km to m, kg to g, L to mL) and vice versa.
- Students will be able to add and subtract measures of length, weight and capacity with regrouping, expressing answers in mixed units.
- Students will be able to estimate the length, weight or capacity of an everyday object and then measure it using a suitable tool, comparing the estimate with the actual measurement.
Lessons in this unit
- Choosing the right unit: Understand which unit (km, m, cm; kg, g; L, mL) is appropriate for measuring different objects and distances. Use real-life examples to build intuition.
- Converting units: Convert between units within the same system: m to cm, km to m, kg to g, L to mL, and the reverse. Use place value understanding (multiplying or dividing by 100 or 1000).
- Adding and subtracting measures: Add and subtract measures of length, weight and capacity with regrouping, expressing answers in mixed units (e.g., 2 m 75 cm + 1 m 50 cm = 4 m 25 cm).
- Estimating and measuring: Estimate the length, weight or capacity of everyday objects and then measure using appropriate tools (ruler, measuring tape, weighing scale, measuring jug). Compare estimates with actual measurements.
Key words
- length
- How long something is from one end to the other.
- weight
- How heavy something is.
- capacity
- How much a container can hold inside.
- kilometre (km)
- A unit for measuring long distances, like the distance between two cities.
- metre (m)
- A unit for measuring medium lengths, like the height of a door.
- centimetre (cm)
- A small unit for measuring short lengths, like the length of a pencil.
- kilogram (kg)
- A unit for measuring heavy things, like a sack of rice.
- gram (g)
- A small unit for measuring light things, like a paperclip.
- litre (L)
- A unit for measuring liquids, like a bottle of water.
- millilitre (mL)
- A very small unit for measuring tiny amounts of liquid, like a spoon of medicine.
- convert
- To change from one unit to another without changing the amount, like changing 100 cm to 1 m.
Help your child at home
What to watch for
- Using 'cm' for long distances like a road.
- Help: Show a metre scale and a map; explain that a road is many metres, so we use km.
- 1 m = 1000 cm (confusing with km).
- Help: Use a metre scale: 1 m has 100 cm. Show 100 cm on the scale.
- Adding 75 cm + 50 cm gives 125 cm, but they write 1 m 25 cm incorrectly as 12 m 5 cm.
- Help: Show that 125 cm = 100 cm + 25 cm = 1 m 25 cm.
- Estimating means guessing randomly without any reasoning.
- Help: Teach them to compare with known objects (e.g., a pencil is about 15 cm, so a book is about 30 cm).
Try this at home
- Match the object to the unit
- Convert m to cm
- Add lengths: 2 m 75 cm + 1 m 50 cm
- Estimate and measure the length of a pencil
Quick questions to ask aloud
- Which unit is best to measure the length of a pencil? (centimetre (cm) / metre (m) / kilometre (km))
Show answer
centimetre (cm). A pencil is about 15 cm long, so centimetre is the best unit. - How many centimetres are there in 3 metres?
Show answer
1 m = 100 cm, so 3 m = 3 × 100 = 300 cm. - Add: 2 m 75 cm + 1 m 50 cm. Write the answer in metres and centimetres (e.g., 3 m 40 cm).
Show answer
75 cm + 50 cm = 125 cm = 1 m 25 cm. Add the metres: 2 m + 1 m + 1 m = 4 m. So total is 4 m 25 cm.
Frequently asked questions
What will my child learn in "Length, Weight and Capacity" (Class 4 Maths)?
Your child will be able to: choose the appropriate standard unit (km, m, cm; kg, g; L, mL) for measuring a given object or distance.; convert between units within the same system (m to cm, km to m, kg to g, L to mL) and vice versa.; add and subtract measures of length, weight and capacity with regrouping, expressing answers in mixed units.; estimate the length, weight or capacity of an everyday object and then measure it using a suitable tool, comparing the estimate with the actual measurement..
How does MangoMindz teach "Length, Weight and Capacity"?
In 4 short parts (Choosing the right unit, Converting units, Adding and subtracting measures, Estimating and measuring). Each part has a picture-based lesson read aloud by Mango Teacher, a quick check, and a quiz built from common mistakes children make, with Mango, a study buddy, for questions.
How long does "Length, Weight and Capacity" take?
About 120 minutes in total, spread over 4 parts of 15–25 minutes each.
How can I help my child with "Length, Weight and Capacity" at home?
Work through a small example together, such as: Match the object to the unit; Convert m to cm. Then ask a quick question aloud: Which unit is best to measure the length of a pencil? (centimetre (cm) / metre (m) / kilometre (km))
What mistakes do children often make in "Length, Weight and Capacity"?
Using 'cm' for long distances like a road. Fix: Show a metre scale and a map; explain that a road is many metres, so we use km. 1 m = 1000 cm (confusing with km). Fix: Use a metre scale: 1 m has 100 cm. Show 100 cm on the scale. Adding 75 cm + 50 cm gives 125 cm, but they write 1 m 25 cm incorrectly as 12 m 5 cm. Fix: Show that 125 cm = 100 cm + 25 cm = 1 m 25 cm.
Is "Length, Weight and Capacity" free on MangoMindz?
Yes. Every lesson part and quiz in "Length, Weight and Capacity" is free on MangoMindz, with no ads.