Measuring Length
Class 4 · Mathematics
4 ideas in Class 4 Mathematics, explained in plain words, with games and quizzes to practise.
Metre, Half Metre and Quarter Metre
Part of: Measuring with ropes and scales
A metre is a standard length for measuring things like a room or a playground. Fold a metre-long string in half and each piece is half a metre. Fold it in half again and each piece is a quarter of a metre. Four quarters make one whole metre.
Why it matters. Children need a feel for how long a metre is before they can estimate and compare lengths around them. Without it, longer distances stay vague guesses.
Try it in two minutes
- Take a string or a strip of paper about one metre long and show it to your child.
- Fold it in half. Ask: how long is each piece now?
- Fold it in half once more. Ask: how many of these small pieces make the whole string?
- Lay the whole string end to end along the floor three times. Ask: how long is the line now?
Try at home. Ask your child to guess, then check with the string, how many metres long your hallway or balcony is.
Centimetres and Small Lengths
Part of: Measuring with ropes and scales
A centimetre (cm) is a small unit for measuring little things such as an eraser or a leaf. A metre scale is divided into 100 equal parts and each part is 1 cm. So 1 metre is the same as 100 cm.
Why it matters. Small objects cannot be measured well in metres. Knowing centimetres lets children measure and compare everyday things and read a ruler correctly.
Try it in two minutes
- Give your child a ruler and a few small things like a key, a spoon and a pencil.
- Ask your child to guess each length in cm, then measure to check.
- Show that you must start from the 0 mark and not from the edge of the ruler.
- Ask your child to arrange the objects from shortest to longest.
Try at home. Let your child measure a houseplant or a bean sprout once a week and write the height in cm.
Converting Metres and Centimetres
Part of: Metres and centimetres together
One length can be written in more than one way. A rope of 1 m 35 cm is the same as 135 cm, because 1 m is 100 cm and 35 cm is added to it. To change metres to centimetres, multiply the metres by 100 and add the extra centimetres.
Why it matters. Children meet heights and distances written both ways. Without conversion they cannot compare a height of 1 m 40 cm with one of 135 cm.
Try it in two minutes
- Measure the height of your child with a tape. Say it as metres and centimetres, for example 1 m 18 cm.
- Ask: how many cm is that in all? Show that 1 m is 100 cm and the extra 18 cm are added.
- Measure a family member and compare the two heights, once in cm and once in m and cm.
- Ask: who is taller and by how many cm?
Try at home. Make a height chart on a wall or paper with every family member's height written in both m and cm.
Perimeter of a Shape
Part of: Perimeter
The perimeter is the total length around the edge of a closed shape. Imagine walking once around a table top. The distance you walk is its perimeter. To find it, add up the lengths of all the sides.
Why it matters. Perimeter is used for fencing a garden, putting a border on a picture or lacing a frame. Children who only add two sides get the wrong length.
Try it in two minutes
- Pick a book or a plate mat and a piece of string.
- Run the string once around the edge and cut it where it meets.
- Straighten the string and measure it with a ruler. That is the perimeter.
- Now measure each side of the book, add them up and see if you get the same answer.
Try at home. Ask your child to find which has the longer perimeter, the cover of a notebook or a small plate mat.
What your child will practise
- Centimetres and Small Lengths: Candy Puzzle (Clue Puzzle)
- Centimetres and Small Lengths: Ocean Sort (Sort It Out)
- Converting Metres and Centimetres: Jungle Quest (Flip and Match)
- Metre, Half Metre and Quarter Metre: Ocean Quest (Collect the Answer)
- Perimeter of a Shape: Ocean Quick Fire (Quick Fire)
- Quiz: Centimetres and Small Lengths (8 questions)
- Quiz: Converting Metres and Centimetres (8 questions)
- Quiz: Metre, Half Metre and Quarter Metre (8 questions)
- Quiz: Perimeter of a Shape (8 questions)