Measures
Length
In this unit you measure how long, wide or tall things are. You use centimetres for shorter lengths and metres for longer ones, and you learn to find the difference between two lengths.
Centimetres and metres
We measure length in centimetres (cm) and metres (m). Centimetres are best for shorter lengths, like a pencil. Metres are best for longer lengths, like the height of a door. A metre is longer than a centimetre. 1 metre is made of 100 centimetres.
Length, width and height
The length of an object is the distance from one end to the other along its longest side. The width is the distance along the shorter side. The height is how tall or high something is.
Using a ruler
Look at the edge of your ruler. On some rulers the 0 is right at the edge. On others the 0 mark is a little way in. Always start measuring from the 0 mark. Each number on the ruler stands for one centimetre. If a bar does not start at 0, count from where it starts to where it ends.
Finding the difference
To find the difference between two lengths, take the smaller one away from the bigger one. Example: a rope is 24 m long. If 14 m is cut off, the difference is 24 - 14 = 10 m left.
Worked examples
Compare two lengths
- A pencil is 12 cm and a crayon is 8 cm.
- Compare the numbers: 12 is more than 8.
- So the pencil is longer and the crayon is shorter.
Answer: The pencil (12 cm) is longer than the crayon (8 cm).
Choose the right unit
- Think about how long the thing is.
- A pencil is short, so measure it in centimetres.
- A door is tall, so measure it in metres.
Answer: Centimetres for short lengths, metres for long lengths.
Measure a bar on the ruler
- Look at where the bar starts and where it ends.
- This bar starts at 2 cm and ends at 9 cm.
- Count from the start: 9 - 2 = 7.
Answer: The bar is 7 cm long.
Find the difference between two lengths
- One ribbon is 24 cm and another is 18 cm.
- Take the smaller away from the bigger: 24 - 18.
- 24 - 18 = 6.
Answer: The difference is 6 cm.
Where you see this in real life
- Measuring how tall you are with a metre ruler to see if you are just over or just under 1 metre.
- Using a ruler to measure the width of your table in centimetres.
- Working out how much rope is left after some is cut off.
Key words
- Length
- The distance from one end of an object to the other along its longest side.
- Width
- The distance across the shorter side of an object.
- Height
- How tall or high something is.
- Centimetre (cm)
- A small unit of length. Best for measuring short things.
- Metre (m)
- A longer unit of length. 1 metre is 100 centimetres.
- Estimate
- A sensible guess about how long something is, made before you measure.
- Difference
- How much longer one length is than another, found by subtracting.