1. What is mass?

Mass tells us how heavy something is. It is the amount of matter in an object. Mass is different from size — a small rock can be heavier than a big balloon.

2. Units of mass

• Gram (g) — good for small things (a paper clip is about 1 g).
• Kilogram (kg) — 1 kg = 1000 g. Used for heavier things (a bag of maize flour might be 2 kg or 10 kg).

Write this: 1 kg = 1000 g. So 0.5 kg = 500 g.

3. How we measure mass

We use scales. There are kitchen scales and bathroom scales or balance scales in school.

You read the numbers on the scale to know the mass.

4. Everyday Kenyan examples

• A packet of sugar might be 1 kg.
• A small avocado (parachichi) might be about 200 g.
• A litre jerrycan of water weighs about 1 kg (because 1 litre of water ≈ 1 kg).
• A big bag of maize flour could be 2 kg, 5 kg, or 10 kg.

5. Converting kg and g — easy steps

To change kg to g: multiply by 1000. Example: 3 kg = 3 × 1000 = 3000 g.

To change g to kg: divide by 1000. Example: 2500 g = 2500 ÷ 1000 = 2.5 kg.

6. Practice questions

1. Write 1 kilogram as grams.
2. A mango weighs about 250 g. How many mangoes make 1 kg?
3. Change 4500 g to kilograms.
4. A packet of rice is 2 kg. If you buy 3 packets, what is the total mass in kg?
5. Estimate then check: Which is heavier — a small stone or a small packet of salt (about 50 g)? Try weighing at home.

7. Fun activity for class or home

Make a guessing game: students estimate the mass of items (banana, book, small water bottle), then measure with a scale. Record estimates and actual masses. Talk about why estimates were close or far.