Length & Weight
Measurement, Money & Data: Length & Weight
Length & Weight
Length & Weight
What you'll learn
- Standard units of length: centimetre (cm) and metre (m), where 1 m = 100 cm.
- Standard units of weight: gram (g) and kilogram (kg), where 1 kg = 1000 g.
- To add and subtract lengths and weights given in the same or mixed units.
Key concepts
Level 1 — Core idea
Verbal: A metre is a bigger unit made of 100 centimetres, just like a kilogram is made of 1000 grams.
Symbolic: 1 m = 100 cm; 1 kg = 1000 g.
Visual: A metre scale is marked from 0 to 100 in centimetres; a 1 kg weight balances 1000 g of rice on a scale.
Level 2 — Going deeper
To add or subtract mixed measurements (like 2 m 35 cm + 1 m 40 cm), first convert everything into the smaller unit (cm or g), do the arithmetic, then convert back if needed.
NCERT anchor
NCERT Math Mela, Class 3 — Chapter 4 (Long and Short) and Chapter 12 (Time Goes On... / Weight) introduce measuring length with a scale and weighing objects using a balance.
Worked example
A rope is 3 m long. How many centimetres is that?
Step 1 — 1 m = 100 cm
Step 2 — 3 m = 3 × 100 = 300 cm
Answer: 300 cm
A bag of sugar weighs 2 kg. 350 g is used for a cake. How much sugar is left, in grams?
Step 1 — Convert: 2 kg = 2000 g
Step 2 — Subtract: 2000 − 350 = 1650 g
Answer: 1650 g
Common mistakes
| Mistake | Why | Fix |
|---|---|---|
| Thinking 1 m = 10 cm | Confusing with tens place-value facts | Remember: 1 m = 100 cm (like 1 rupee = 100 paise) |
| Adding metres and centimetres directly without converting | Treating mixed units like plain numbers | Convert to the same unit first, then add or subtract |
| Mixing up kg and g when reading a weighing scale | Not checking the unit label | Always check whether the scale shows grams or kilograms |
Quick check
- How many centimetres are there in 5 m?
- How many grams are there in 4 kg?
- A ribbon is 6 m long; 250 cm is cut off. How much ribbon is left, in cm?
- Stretch: Two sacks weigh 3 kg 200 g and 2 kg 500 g. What is their total weight? (5 kg 700 g)
Revision tip: Convert bigger units to smaller units (m → cm, kg → g) before adding or subtracting mixed measurements.
Open the Practice tab for graded questions on Length & Weight.
Key Takeaways (TL;DR)
- What you'll learn
- Key concepts
- Worked example
- Common mistakes
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