Grade 4 Mathematics Measurement – Length Notes

What is length?

Length tells us how long something is. We measure length from one end to the other end. We measure using units like metres and centimetres.

Common units of length

• Millimetre (mm) — small unit. 10 mm = 1 cm.
• Centimetre (cm) — good for pencils, rulers. 100 cm = 1 m.
• Metre (m) — used for doors, classroom length, people height.
• Kilometre (km) — used for distance between towns (e.g., Nairobi to Nakuru ~ 160 km).

Important conversions

Remember these:

• 1 m = 100 cm
• 1 cm = 10 mm
• 1 km = 1000 m

How to measure

1. Place the ruler or tape so the zero mark is at one end.
2. Look at the other end and read the number at the mark.
3. For parts of a unit (half a metre), read the smaller marks (e.g., 50 cm = 0.5 m).

Simple ruler picture (shows marks)

Visual comparison (approximate)

Below are colour bars that help you see which object is longer.

Worked examples

Example 1: A pencil is 15 cm long. How many centimetres are in 1 metre?

Answer: 1 m = 100 cm, so 15 cm is 0.15 m or 15 cm remains 15 cm.

Example 2: Convert 150 cm to metres.

Method: 100 cm = 1 m → 150 cm = 100 cm + 50 cm = 1 m + 50 cm = 1 m 50 cm = 1.5 m.

Example 3: Convert 3.2 m to cm.

Method: 1 m = 100 cm → 3.2 m = 3.2 × 100 = 320 cm.

Practice questions

1. How many centimetres are in 2 metres?
2. Write 75 cm as metres and centimetres.
3. Convert 5 km to metres.
4. If a classroom is 8 m long, how many centimetres long is it?
5. A rope is 250 cm. What is its length in metres?

1. 2 m = 200 cm.
2. 75 cm = 0 m 75 cm or 0.75 m.
3. 5 km = 5 × 1000 m = 5000 m.
4. 8 m = 8 × 100 cm = 800 cm.
5. 250 cm = 2 m 50 cm = 2.5 m.

Fun activity to try at home or school

Use a tape measure or metre stick. Measure these and write the answers in cm and m:

• Height of a door
• Length of your school bag
• Width of the classroom
• Distance from classroom door to the school gate (estimate in m)