Perimeter and area · Usually met around P4
Counting perimeter
Count piece by piece: across, then up and down.
How to do it
Method
Count piece by piece: across, then up and down
Across 4 + 4, up 3 + 3: perimeter 14 cm
Another way
Push out to a rectangle
2 × (4 + 3) = 14
In full
Perimeter is the distance once round the edge of a shape. On squared paper each side of a square is 1 cm: follow the edge piece by piece all the way round and count, and the count is the perimeter in cm. Count the across edges first, then the up-and-down ones, and add: that way none is missed. To compare two shapes' perimeters, compare the distances round each; a bigger area doesn't always mean a longer perimeter. Another way: push the steps of a staircase edge out to make a rectangle, which keeps the perimeter the same: 2 × (length + width), plus any part that can't be pushed out.
Worked examples
Have a go first, then open each one for the answer and the working.
Example 1
Each square on the paper is 1 cm a side. What is the perimeter of the shape in cm?
Show the answer and working
Answer: 14 cm
Follow the edge piece by piece, across and up and down: 14 pieces round, so 14 cm.
Example 2
Squares 1 cm a side are laid in 2 rows of 4 to make a rectangle. What is its perimeter?
- A. 16 cm
- B. 12 cm
- C. 8 cm
- D. 6 cm
Choose the right answer
Show the answer and working
Answer: B. 12 cm
4 cm long and 2 cm wide: once round is 4 + 2 + 4 + 2 = 12 cm.
Example 3
Each square on the paper is 1 cm a side. What is the perimeter of the shape in cm?
Show the answer and working
Answer: 20 cm
Across: 5 pieces top and bottom. Up and down: both ends and every step: 20 cm in all.
Practise it in the game →Perimeter and area · Free to start, unlimited questions, no download