Grade 5 Mathematics Measurement – Mass Notes
Mathematics — Measurement
Subtopic: Mass (for learners aged 10 — Kenyan context)
What is Mass?
Mass is the amount of matter in an object. We measure mass to know how heavy something is. In Kenya and in science we usually use the kilogram (kg) and the gram (g).
Common units of mass
- Tonne (t) — used for very heavy things (e.g., a lorry load). 1 t = 1,000 kg.
- Kilogram (kg) — used for bags of maize, sugar, people (e.g., a sack of maize is 50 kg).
- Gram (g) — used for small items (e.g., fruits, biscuits). 1 kg = 1,000 g.
- Milligram (mg) — very small mass. 1 g = 1,000 mg.
Key conversions
- 1 kg = 1,000 g
- 1 g = 1,000 mg
- 1 t (tonne) = 1,000 kg
- 1 g = 1,000 mg
- 1 t (tonne) = 1,000 kg
Measuring tools
- Balance scales (two pans) — used in shops and labs.
- Spring scales / digital scales — used at home and supermarkets.
Simple balance picture
500 g
0.5 kg
The two pans are balanced: 500 g = 0.5 kg.
Worked examples
Example 1: Convert 2 kg into grams.
Step: 1 kg = 1,000 g → 2 kg = 2 × 1,000 g = 2,000 g.
Answer: 2 kg = 2,000 g.
Step: 1 kg = 1,000 g → 2 kg = 2 × 1,000 g = 2,000 g.
Answer: 2 kg = 2,000 g.
Example 2 (Kenyan context): A sack of maize weighs 50 kg. How many grams is this?
Step: 50 kg × 1,000 = 50,000 g.
Answer: 50 kg = 50,000 g.
Step: 50 kg × 1,000 = 50,000 g.
Answer: 50 kg = 50,000 g.
Example 3: Convert 750 g to kilograms.
Step: 1,000 g = 1 kg → 750 g = 750 ÷ 1,000 = 0.75 kg.
Answer: 750 g = 0.75 kg.
Step: 1,000 g = 1 kg → 750 g = 750 ÷ 1,000 = 0.75 kg.
Answer: 750 g = 0.75 kg.
Tips for converting
- To change kg → g: multiply by 1,000 (move the decimal 3 places right).
- To change g → kg: divide by 1,000 (move the decimal 3 places left).
- Use examples from home: sugar packet (2 kg), mango ~200 g, a child’s school bag maybe 3–5 kg.
Practice questions
- Convert 3 kg to grams.
- Convert 2,500 g to kilograms.
- A bag of rice is 10 kg. How many grams is this?
- An apple weighs 150 g. Two apples weigh how many grams and how many kilograms?
- A lorry carries 4 tonnes of maize. How many kilograms is this?
- Change 5,250 g into kg and g (write as 'x kg y g').
- If a packet of sugar is 2 kg and you buy 3 packets, what is the total mass in kg and in grams?
- Which is heavier: 900 g or 0.9 kg? Explain briefly.
Answers
1) 3 kg = 3,000 g.
2) 2,500 g = 2.5 kg.
3) 10 kg = 10,000 g.
4) Two apples = 300 g = 0.3 kg.
5) 4 t = 4 × 1,000 kg = 4,000 kg.
6) 5,250 g = 5 kg 250 g.
7) 3 × 2 kg = 6 kg = 6,000 g.
8) They are equal: 900 g = 0.9 kg. (900 ÷ 1000 = 0.9)
2) 2,500 g = 2.5 kg.
3) 10 kg = 10,000 g.
4) Two apples = 300 g = 0.3 kg.
5) 4 t = 4 × 1,000 kg = 4,000 kg.
6) 5,250 g = 5 kg 250 g.
7) 3 × 2 kg = 6 kg = 6,000 g.
8) They are equal: 900 g = 0.9 kg. (900 ÷ 1000 = 0.9)
Short activity for the classroom or at home
Pick five items at home (e.g., potato, mango, book, sugar packet, school bag). Use a scale to measure each in kg or g. Record your answers and convert each into the other unit (kg → g or g → kg).
Note for teacher/parent: At this age focus on practice with real objects and scales. Reinforce the idea that mass is the same anywhere (mass does not change if you go to another place), while weight can change with strong differences in gravity (no need for deep details now).