What you will learn
- Choose grams or kilograms, and say why a gram is needed.
- Convert between kilograms and grams: 1 kg = 1 000 g.
- Read a scale, compare masses and solve mass problems, including labels on packets.
A bag of rice and a pencil are both things you can pick up, but a kilogram bag is a poor unit for the pencil. The pencil needs a smaller unit, the gram. In this lesson mass means how heavy something is. On a packet you may see the word weight. We will read that number as the mass. You will convert grams and kilograms, read a scale and use masses in problems.
Grams and kilograms
The kilogram (kg) is the unit for heavier things: a bag of flour, a school bag, a child. A child in Standard 3 might have a mass of about 30 kg. The gram (g) is for lighter things: a pencil, a mango, an exercise book. A small paper clip is about 1 g. We need grams because a kilogram is too big for those objects. Saying a pencil is 0 kg would hide its real mass.
| Object | Best unit |
|---|---|
| a paper clip | g |
| a mango | g |
| a 2 kg bag of rice | kg |
| a Standard 3 child | kg |
Worked example 1
Which unit is better for a mango, g or kg? Which is better for a packed school bag?
Show me how
A mango is light. One kilogram is about the mass of a big bottle of water, and a mango is less than that.
A packed school bag is several kilograms.
Use grams for the mango and kilograms for the school bag.
Changing units
1 kg = 1 000 g. To change kilograms into grams, multiply by 1 000. To change grams into kilograms, see how many groups of 1 000 you have.
2 kg = 2 000 g. 3 kg 250 g = 3 250 g. 1 500 g = 1 kg 500 g. 4 000 g = 4 kg.
Worked example 2
A packet of flour is labelled 2 kg. How many grams is that? Another packet is labelled 750 g. Which is heavier?
Show me how
2 kg = 2 × 1 000 g = 2 000 g.
2 000 g is more than 750 g.
The 2 kg packet is heavier. It has mass 2 000 g.
Watch out! A common mistake
1 kg is 1 000 g, not 100 g. 100 g is only a tenth of a kilogram. If you remember that 1 km = 1 000 m, use the same thousand for 1 kg = 1 000 g.
Reading a scale
Look at the unit first. Then read the mark the pointer is on. On this scale the long marks are every 200 g and the short marks are every 100 g.
The pointer is on 600. The mass is 600 g.
The pointer is on the short mark at 300. The mass is 300 g.
If two sides of a balance are level, the masses are equal. If one side goes down, that side has the greater mass.
Worked example 3
A scale is marked in grams and the pointer is at 800. What is the mass? Is it more or less than 1 kg?
Show me how
Read the pointer: 800 g.
1 kg = 1 000 g, and 800 is less than 1 000.
The mass is 800 g, which is less than 1 kg.
Packets and problems
Food packets print the mass. Read the number and the unit. Do not mix g and kg when you add. Change them to the same unit first.
Two tins of 400 g have mass 400 + 400 = 800 g. A 2 kg bag of rice has mass 2 000 g, so the bag is heavier than the two tins.
Worked example 4
Tomatoes cost 6 dollars a kilogram. Dad buys 3 kg. What is the mass in grams, and what is the cost?
Show me how
3 kg = 3 000 g.
Cost = 3 × 6 dollars = 18 dollars.
The tomatoes have mass 3 000 g and cost 18 dollars.
Try it
TRY ITMass lab
Choose grams or kilograms, convert, read a scale, compare two masses and solve a problem.
Let’s practise
Work out each one in your copybook. Open Hint if you are stuck, then open Show answer to check your working.
1. Why do we need grams as well as kilograms?
Hint
Think of a paper clip.
Show answer
A kilogram is too big for light objects. Grams let us measure them.
2. Which unit is better for a packed school bag, g or kg?
Hint
A school bag is much heavier than a pencil.
Show answer
kg
3. How many grams are in 4 kg?
Hint
1 kg = 1 000 g.
Show answer
4 000 g
4. Write 2 500 g in kilograms and grams.
Hint
How many groups of 1 000 are in 2 500?
Show answer
2 kg 500 g
5. A scale marked in grams shows 700. What is the mass?
Hint
Read the pointer.
Show answer
700 g
6. Which is heavier, 900 g or 1 kg?
Hint
Change 1 kg into grams first.
Show answer
1 kg is heavier, because 1 000 g is more than 900 g.
7. Two packets are 250 g each. What is the total mass?
Hint
Add the two masses.
Show answer
500 g
8. Flour costs 4 dollars a kilogram. What is the cost of 5 kg?
Hint
Multiply the price by the number of kilograms.
Show answer
20 dollars
Quiz
Lesson quiz: 10 questions
Answer every question, then press Check my answers. Score 8 or more to earn the Mass Master badge.
Mass: worksheet
Name: ____________________ Date: ______________
Part A: Let’s practise
1. Why do we need grams as well as kilograms?
2. Which unit is better for a packed school bag, g or kg?
3. How many grams are in 4 kg?
4. Write 2 500 g in kilograms and grams.
5. A scale marked in grams shows 700. What is the mass?
6. Which is heavier, 900 g or 1 kg?
7. Two packets are 250 g each. What is the total mass?
8. Flour costs 4 dollars a kilogram. What is the cost of 5 kg?
Part B: Quiz
1. The best unit for the mass of a mango is
(a) km
(b) m
(c) g
(d) kg
2. How many grams are in 3 kilograms?
3. 1 500 g is the same as
(a) 1 kg 500 g
(b) 15 kg
(c) 150 kg
(d) 1 kg 50 g
4. 1 kilogram = 100 grams.
True or False? Circle one: True / False
5. A scale is marked in grams and the pointer is at 400. What is the mass in grams?
6. A packet says 2 kg. How many grams is that?
(a) 20 g
(b) 2 000 g
(c) 200 g
(d) 2 g
7. A paper clip has a mass of about 1 kg.
True or False? Circle one: True / False
8. Two tins have mass 400 g each. How many grams is that altogether?
9. Which mass is the greatest?
(a) 500 g
(b) 1 kg
(c) 200 g
(d) 2 kg
10. Tomatoes cost 6 dollars a kilogram. How many dollars do 3 kg cost?
Answers (for the adult)
Part A
1. A kilogram is too big for light objects. Grams let us measure them.
2. kg
3. 4 000 g
4. 2 kg 500 g
5. 700 g
6. 1 kg is heavier, because 1 000 g is more than 900 g.
7. 500 g
8. 20 dollars
Part B
1. (c) g
2. 3000
3. (a) 1 kg 500 g
4. False
5. 400
6. (b) 2 000 g
7. False
8. 800
9. (d) 2 kg
10. 18
Recap
- Use grams for light objects and kilograms for heavier ones.
- 1 kg = 1 000 g. Multiply by 1 000 to change kg into g.
- Read the unit on a scale, then read the pointer.
- Change masses to the same unit before you add or compare them.
- A packet label gives the mass and the unit. Read both.
Words to know
- mass
- How heavy something is.
Example: The mass of the flour is 2 kg. - gram (g)
- A small unit of mass. 1 000 g make 1 kg.
Example: A mango is measured in grams. - kilogram (kg)
- A unit of mass for heavier objects.
Example: The rice has mass 2 kg. - scale
- A tool that measures mass.
Example: The kitchen scale shows 600 g. - balance
- A scale with two sides. Level sides mean equal masses.
Example: The balance was level, so the masses matched.
Try it at home
- Find five food packets in the kitchen. Write the mass on each one and say whether it is in g or kg.
- Pick one object lighter than 1 kg and one heavier than 1 kg. Explain how you decided.
Test tips
Tips for class tests
- Write g or kg every time. 2 could mean 2 g or 2 kg.
- Change to the same unit before you compare. 1 kg is 1 000 g, not 100 g.
- On a scale, name the unit printed on it before you read the pointer.
For parents and teachers
After this lesson, your child should be able to:
- choose grams or kilograms and explain why a unit smaller than the kilogram is needed;
- convert between kilograms and grams and read a simple scale;
- compare masses, read a packet label, and solve problems that use mass, number and money.
In class we say mass. Packets at home often say weight or net weight. It helps if you read the number and the unit together, for example 400 g, and ask whether that is more or less than 1 kg. Estimates such as a paper clip about 1 g, or a child about 30 kg, are for choosing a unit. They are not figures to memorise.
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Previous: Perimeter – Standard 3 Maths
Next: Time: Clocks, Durations and Dates – Standard 3 Maths
Course: Standard 3 Maths
Updates
2026/11/06
– Linked the next lesson, Time: Clocks, Durations and Dates.
– Published this lesson and updated the lesson navigation.
2026/11/05
– First version of this lesson.
Attributions to media used in this post:
Escali digital kitchen scale.jpg – Ser Amantio di Nicolao – CC BY-SA 4.0 (via Wikimedia Commons)
© 2026 Vedesh Kungebeharry. All rights reserved.
