Year 4 Maths: Converting Units of Length

What are Units of Length?

Units of length are ways we measure how long something is. In the UK, we often use millimeters (mm), centimeters (cm), metres (m), and kilometres (km).

• Millimetres (mm): Very small measurements. For example, the width of a pencil.
• Centimetres (cm): A bit bigger. For example, the length of a ruler.
• Metres (m): Used for things like the height of a door.
• Kilometres (km): Used for long distances, like how far it is to school.

How to Convert Units of Length

Key Rules

1. Know the Relationships:
   • 1 centimetre = 10 millimetres
   • 1 metre = 100 centimetres
   • 1 metre = 1,000 millimetres
   • 1 kilometre = 1,000 metres
2. When to Multiply or Divide:
   • If you are changing to a smaller unit, you multiply.
   • If you are changing to a larger unit, you divide.

Examples

1. Converting centimetres to millimetres:
   • If you have 5 cm and want to know how many millimetres that is:
   $$ 5 , \text{cm} \times 10 = 50 , \text{mm} $$
2. Converting metres to kilometres:
   • If you have 2,500 m and want to change it to kilometres:
   $$ 2,500 , \text{m} \div 1,000 = 2.5 , \text{km} $$

Tips and Tricks

• Use a conversion chart: Having a chart can help you see the relationships easily.
• Practice: The more you practice, the better you will get at converting.
• Visualisation: Try to picture the length. For example, a metre is about the height of a door.

Questions for Practice

Easy Level Questions (20 Questions)

1. How many millimetres are in 1 centimetre?
2. Convert 3 cm to mm.
3. How many centimetres are in 1 metre?
4. Convert 2 m to cm.
5. Convert 500 mm to cm.
6. How many millimetres are in 2 cm?
7. Convert 1 m to mm.
8. Convert 150 cm to mm.
9. How many metres are in 200 cm?
10. Convert 4 m to cm.
11. How many centimetres are in 3 m?
12. Convert 1.5 m to cm.
13. How many mm are in 10 cm?
14. Convert 250 mm to cm.
15. How many mm are in 0.5 m?
16. Convert 5 m to mm.
17. How many cm are in 100 mm?
18. Convert 6 cm to mm.
19. How many mm are there in 8 cm?
20. Convert 0.2 m to cm.

Medium Level Questions (20 Questions)

1. Convert 25 cm to mm.
2. If a pencil is 15 cm long, how many mm is that?
3. Convert 3.5 m to cm.
4. How many mm are in 4.2 cm?
5. Convert 750 mm to m.
6. If a table is 2 m long, how many cm is that?
7. Convert 0.7 km to m.
8. How many cm in 5.5 m?
9. Convert 1,200 mm to cm.
10. If a book is 0.3 m tall, how many cm is that?
11. Convert 88 cm to mm.
12. How many m are in 3,600 mm?
13. Convert 4 km to m.
14. If a door is 2.5 m tall, how many mm is that?
15. Convert 30 cm to m.
16. How many cm are in 1.2 m?
17. Convert 98 mm to cm.
18. If you run 1.5 km, how many m is that?
19. Convert 2.2 m to cm.
20. How many mm are in 9.9 cm?

Hard Level Questions (20 Questions)

1. Convert 1500 mm to km.
2. If a garden is 0.5 km long, how many m is that?
3. Convert 120 cm to km.
4. How many mm are in 5.2 m?
5. Convert 0.05 km to m.
6. If a rope is 3.75 m long, how many cm is that?
7. Convert 2,500 mm to m.
8. If a stick is 4.1 m long, how many mm is that?
9. Convert 3.6 km to m.
10. How many cm are in 7.5 m?
11. Convert 1.75 m to cm.
12. If a car travelled 150 km, how many m is that?
13. Convert 2000 mm to km.
14. If a swimming pool is 2.8 m long, how many cm is that?
15. Convert 5.4 km to m.
16. How many mm are in 8.6 m?
17. Convert 0.9 km to cm.
18. If a desk is 120 cm long, how many mm is that?
19. Convert 3.3 m to mm.
20. If a mountain is 1.2 km high, how many m is that?

Answers and Explanations

Easy Level Answers

1. 10 mm
2. 30 mm
3. 100 cm
4. 200 cm
5. 50 cm
6. 20 mm
7. 1,000 mm
8. 1,500 mm
9. 2 m
10. 400 cm
11. 300 cm
12. 150 cm
13. 100 mm
14. 25 cm
15. 500 mm
16. 5,000 mm
17. 10 cm
18. 60 mm
19. 80 mm
20. 20 cm

Medium Level Answers

1. 250 mm
2. 150 mm
3. 350 cm
4. 42 mm
5. 0.75 m
6. 200 cm
7. 700 m
8. 550 cm
9. 120 cm
10. 30 cm
11. 880 mm
12. 3.6 m
13. 4,000 m
14. 2,500 mm
15. 0.3 m
16. 120 cm
17. 9.8 cm
18. 1,500 m
19. 220 cm
20. 990 mm

Hard Level Answers

1. 0.0015 km
2. 500 m
3. 0.0012 km
4. 5,200 mm
5. 50 m
6. 375 cm
7. 2.5 m
8. 4,100 mm
9. 3,600 m
10. 750 cm
11. 175 cm
12. 150,000 m
13. 0.002 km
14. 280 cm
15. 5,400 m
16. 8,600 mm
17. 90,000 cm
18. 120,000 mm
19. 3,300 mm
20. 1,200 m

With these examples and practice questions, you should be well on your way to mastering converting units of length! Happy learning!