Perimeter and area · Usually met around P4
Counting squares for area
Count row by row; two halves make one.
How to do it
Method
Count row by row; two halves make one
8 whole + 2 halves = 9 cm²
Another way
Rectangle less the gaps
4 × 3 = 12, less 3 empty: 9
In full
On squared paper each square is 1 cm², so count the shape's squares to get its area in cm². Count row by row (or column by column) and add, so none is missed. Two half squares make 1 whole: 8 whole squares and 2 halves are 8 + 1 = 9 cm². Another way: count the squares in the rectangle round the shape, then take away the empty ones. Careful: area counts squares, perimeter counts edges; don't mix them up.
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 cm². What is the area of the shape in cm²?
Show the answer and working
Answer: 12 cm²
11 whole squares and 2 halves, two halves to a square: 12 cm².
Example 2
Each square on the paper is 1 cm². The shape's area is 16 cm².
True or false?
Show the answer and working
Answer: False
Area counts squares: 13 of them; 16 is the number of edge pieces, the perimeter.
Example 3
At least how many more squares must be added to fill this shape out into a rectangle (none taken away)?
Show the answer and working
Answer: 6
The smallest rectangle is 4 wide and 4 tall: 4 × 4, less the squares already there, is 6.
Practise it in the game →Perimeter and area · Free to start, unlimited questions, no download