2
Centimeters or meters?
Discover Mathematics P3: Term 1, Lessons 1–10
GoalChoose centimetres or metres for measuring things, and know that 1 m = 100 cm.
New words
metre (m) · a unit of length equal to 100 cmestimate · a careful guess that is close to the real numberunit · the name we write after a measurement, such as cm or m
Explanation
We measure small things in centimetres and big things in metres. A pencil, a key or a coin is measured in cm. A door, a classroom or a bus is measured in m. One metre is 100 centimetres, so 2 m is 200 cm. A child of 8 is a little taller than 1 m. Sometimes a careful guess, an estimate, is good enough, such as deciding if a room is about 5 m long. When we must cut cloth or build a shelf, we need an exact measurement.
Worked examples
A pencil is about 15 cm long. A metre would be far too big a unit for it, so we use centimetres.
The classroom door is about 2 m high. That is the same as 200 cm, but 200 cm is hard to picture, so we say 2 m.
| Metres | Centimetres |
|---|---|
| 1 | 100 |
| 2 | 200 |
| 3 | 300 |
| 5 | 500 |
Class activity
Estimate and check. Choose 6 things at home: a spoon, a shoe, a bed, a table, a window and a door. For each one decide if you would use cm or m, and estimate its length. Then measure with a ruler or a tape and compare the real length with your estimate.
Practice
1
Which unit would you use to measure a key, cm or m?
cm.
2
Which unit would you use for the length of a football pitch?
m, because a pitch is very long.
3
Write cm or m for each: a spoon, a school bus, a toothbrush, a bed.
Spoon: cm. School bus: m. Toothbrush: cm. Bed: m.
4
4 m = ___ cm.
400 cm, because 1 m is 100 cm.
5
Karim has a rope that is 250 cm long. Is it longer or shorter than 2 m?
Longer. 2 m is 200 cm, and 250 cm is more than 200 cm.