Weight & Mass — Grade 4 Mathematics
In Grade 4, we work with decimal mass (e.g., 1.45 kg), convert between grams and kilograms fluently, and solve multi-step problems involving mass in real-world contexts.
Key Conversion
1 kg = 1 000 g
• g → kg: divide by 1 000 • kg → g: multiply by 1 000
Decimal notation examples:
• 2 kg 500 g = 2.5 kg • 3 kg 250 g = 3.25 kg • 750 g = 0.75 kg
• g → kg: divide by 1 000 • kg → g: multiply by 1 000
Decimal notation examples:
• 2 kg 500 g = 2.5 kg • 3 kg 250 g = 3.25 kg • 750 g = 0.75 kg
💡 Mass vs weight: Strictly speaking, mass is measured in kg and g. Weight is a force measured in Newtons. In everyday life (and at primary school) we use these words interchangeably.
Real-World Reference Masses
| Object | Approximate mass |
|---|---|
| Small apple | 150 g = 0.15 kg |
| Bag of sugar | 1 000 g = 1 kg |
| Large bag of flour | 1 500 g = 1.5 kg |
| Average cat | 4 000 g = 4 kg |
| Suitcase allowance | 23 000 g = 23 kg |
Worked Examples
Example 1 — Convert and Express as Decimal
Write 3 kg 450 g as kg using decimals.
- 450 g ÷ 1 000 = 0.45 kg
- 3 + 0.45 = 3.45 kg
Example 2 — Subtract Mixed Units
A parcel weighs 4.8 kg. An item of 1 350 g is removed. What is the new mass?
- Convert 1 350 g → 1.35 kg
- 4.8 − 1.35 = 3.45 kg
Example 3 — Multi-Step Shopping 🛒
A shopper buys 3 packs of rice at 0.75 kg each and a tin of tomatoes at 400 g. What is the total mass in kg?
- 3 × 0.75 kg = 2.25 kg (rice)
- 400 g = 0.4 kg
- 2.25 + 0.4 = 2.65 kg
Practice Questions
1. Convert 5 250 g to kg.
✅ 5 250 ÷ 1 000 = 5.25 kg
2. Write 4 kg 80 g as a decimal in kg.
✅ 80 g = 0.08 kg; total = 4.08 kg
3. A bag has a 5 kg limit. Goods weigh 2.75 kg. How much more can be added in grams?
✅ 5 − 2.75 = 2.25 kg = 2 250 g
4. 6 identical parcels weigh 8.4 kg in total. What does one parcel weigh in grams?
✅ 8.4 ÷ 6 = 1.4 kg = 1 400 g
5. Add 1.35 kg + 860 g. Give your answer in kg.
✅ 860 g = 0.86 kg; 1.35 + 0.86 = 2.21 kg
Key Points to Remember
- 1 kg = 1 000 g — the key conversion for mass.
- g → kg: divide by 1 000; kg → g: multiply by 1 000.
- Decimal mass: 3 kg 250 g = 3.25 kg.
- Always convert to the same unit before adding or subtracting.
- Check units in your answer — the question often tells you which unit to use.