Measure area in square centimetres & metres
Theory
Measuring area in square centimetres and square metres is a Year 4 skill: finding how much flat surface a shape covers by counting square units. This page explains the square centimetre (\(\text{cm}^2\)) and the square metre (\(\text{m}^2\)), how to count squares on a grid, and how to choose the right unit for small and large surfaces. In Western Australia square centimetres and square metres are taught in Year 5. Curriculum: VC2M4M02 / AC9M4M02.
Area is the amount of flat surface a shape covers. We measure area by covering the shape with equal square units and counting them.
A square centimetre is a square that is 1 cm long and 1 cm wide. We write it as \(\text{cm}^2\). A square metre is a square that is 1 m long and 1 m wide, written as \(\text{m}^2\). The small 2 shows the unit is a square, not a length.
Choose the unit to match the size of the surface. Use \(\text{cm}^2\) for small surfaces like a card or a photo, and \(\text{m}^2\) for large surfaces like a floor or a garden. Area is different from perimeter, which is the distance around the outside.
Area does not need a formula at this stage, but these unit facts help you count and choose.
How to measure the area of a shape
- Choose the unit. Pick \(\text{cm}^2\) for a small surface or \(\text{m}^2\) for a large one.
- Cover with squares. Line the shape with equal square units on a grid, with no gaps and no overlaps.
- Count the squares. Count them row by row and add. The total is the area, written with the square unit.
- Halves and part squares. Two half squares make one whole. A triangle cut from a rectangle corner to corner is half the rectangle. For a curved shape, count the full squares, then add about half for each part square to estimate.
- Shapes made of rectangles. Find the area of each part, then add.
| \(3\text{ rows of }6\) | \(=\) | \(6+6+6\) |
| \(\text{area}\) | \(=\) | \(18\text{ cm}^2\) |
The area is \(18\text{ cm}^2\).
A playground is a large surface. Square centimetres would need many thousands of tiny squares, so square metres are the sensible choice.
The best unit is \(\text{m}^2\).
| \(4+3+2\) | \(=\) | \(9\) |
| \(\text{area}\) | \(=\) | \(9\text{ cm}^2\) |
The area is \(9\text{ cm}^2\).
| \(3\text{ rows of }9\) | \(=\) | \(9+9+9\) |
| \(\text{area}\) | \(=\) | \(27\text{ m}^2\) |
The area is \(27\text{ m}^2\).
| \(\text{rectangle}\) | \(=\) | \(2 \times 5 = 10\text{ cm}^2\) |
| \(\text{half of } 10\) | \(=\) | \(5\) |
| \(\text{triangle}\) | \(=\) | \(5\text{ cm}^2\) |
The diagonal cuts the rectangle into two equal triangles, so each one is half the area.
| \(8 \times 2\) | \(=\) | \(16\text{ m}^2\) |
| \(3 \times 3\) | \(=\) | \(9\text{ m}^2\) |
| \(16 + 9\) | \(=\) | \(25\text{ m}^2\) |
Find the area of each rectangle, then add them. The garden is \(25\text{ m}^2\).
| \(10 \text{ full}\) | \(=\) | \(10\text{ cm}^2\) |
| \(8 \text{ part squares}\) | \(\approx\) | \(4\text{ cm}^2\) |
| \(10 + 4\) | \(=\) | \(14\) |
Count each part square as about half. The area is about \(14\text{ cm}^2\): more than \(10\) and less than \(18\).
| \(A\) | \(=\) | \(2 \times 9 = 18\text{ cm}^2\) |
| \(B\) | \(=\) | \(3 \times 6 = 18\text{ cm}^2\) |
Yes. Different shapes can have the same area: both are \(18\text{ cm}^2\).
Common pitfalls
Frequently asked questions
What is a square centimetre?
A square centimetre is a square that is 1 cm long and 1 cm wide. It is a unit of area, written as \(\text{cm}^2\). One square centimetre covers exactly one square on a centimetre grid.
How do you find area by counting squares?
Cover the shape with equal squares and count how many fit inside. If a shape has 3 rows of 6 squares, count \(6+6+6=18\) square units.
What is the difference between area and perimeter?
Area is the amount of surface a shape covers, counted in square units. Perimeter is the distance all the way around the outside, counted in length units. Area counts the inside squares, not the edge.
When do you use square metres instead of square centimetres?
Use \(\text{cm}^2\) for small surfaces such as a card or a photo. Use \(\text{m}^2\) for large surfaces such as a floor, a garden or a car park. Square metres save you counting thousands of tiny squares.
How do you write square centimetres and square metres?
Square centimetres are written as \(\text{cm}^2\) and square metres as \(\text{m}^2\). The little 2 shows the unit is a square, not a length.
How do you find the area of an L-shape?
Count the shaded squares row by row and add them, or split the L into two rectangles, find each area and add. An L made of a \(6\) cm by \(3\) cm rectangle and a \(4\) cm by \(4\) cm square has an area of \(18 + 16 = 34\text{ cm}^2\).