📏 Measurement: Length
Units of length from small to big: mm, cm, m, km
▶ Play Door 10Units of Length
We measure how long something is using units. From small to big:
• millimetre (mm) — very tiny, like the thickness of a coin.
• centimetre (cm) — your finger is about 1 cm wide.
• metre (m) — about the height of a door handle from the floor.
• kilometre (km) — a long distance you walk or drive.
We use a ruler to measure short lengths in cm and mm.
Worked example
Problem: Which unit best measures the length of a pencil?
- Centimetres (cm) — a pencil is about 15 cm long.
Answer: Centimetres (cm) — a pencil is about 15 cm long.
Comparing & Converting Length
Useful conversions to remember:
• 1 cm = 10 mm
• 1 m = 100 cm
• 1 km = 1000 m
To change metres to centimetres, multiply by 100. To compare two lengths, make them the same unit first.
Worked example
Problem: How many centimetres in 3 metres?
- 3 × 100 = 300 cm.
Answer: 3 × 100 = 300 cm.