Length — Grade 2 Mathematics
In Grade 2, we extend our understanding of length to include a third unit — the kilometre — for measuring long distances. We practise converting between millimetres, centimetres, metres, and kilometres, and we use these skills to solve real-world problems such as comparing distances and calculating total lengths.
Units of Length
| Unit | Symbol | Best Used For | Equivalent |
|---|---|---|---|
| Millimetre | mm | Very small objects (ant, pin) | 10 mm = 1 cm |
| Centimetre | cm | Pencils, books, rulers | 100 cm = 1 m |
| Metre | m | Room lengths, height of a person | 1000 m = 1 km |
| Kilometre | km | Roads, cities, running races | 1 km = 1000 m |
cm → mm: × 10 | m → cm: × 100 | km → m: × 1000
Worked Examples
Convert 450 cm to metres and centimetres.
- 100 cm = 1 m
- 450 ÷ 100 = 4.5 m
- OR: 4 metres and 50 centimetres
Road A is 3.2 km. Road B is 4100 m. Which road is longer?
- Convert both to metres: 3.2 km = 3200 m
- Compare: 3200 m vs 4100 m
- 4100 m > 3200 m → Road B is longer
A school corridor is measured as 28 m. Express this in (a) centimetres and (b) kilometres.
- (a) 28 m × 100 = 2,800 cm
- (b) 28 m ÷ 1000 = 0.028 km
Practice Questions
Try these! Work out the answers first, then check.
1. Convert 5 km to metres.
2. Convert 350 cm to metres.
3. Which is longer: 2.5 km or 2350 m?
4. A fence uses three pieces of wood: 3 m, 250 cm, and 80 cm. What is the total length in metres?
5. How many centimetres are in 2.75 m?
Key Points to Remember
- Units in order (smallest to largest): mm → cm → m → km.
- 10 mm = 1 cm | 100 cm = 1 m | 1000 m = 1 km.
- To convert to a smaller unit: multiply. To a larger unit: divide.
- Always convert to the same unit before comparing lengths.
- Kilometres are used for long distances (e.g., city-to-city, marathon = 42.2 km).