Year 7
Calculate perimeter and area accurately, define key 2D shapes, choose suitable metric or imperial units, and use simple measurement conversions.
Geometry - perimeter, area and measurement systems
Perimeter measures the distance around a shape, so we add side lengths. Area measures the space inside a shape, so we count or calculate square units. Rectangles, triangles and parallelograms are important 2D shapes because their side structure connects directly to perimeter and area formulas. Measurement units also matter: metric units are linked by powers of 10, while imperial units are still common in some real-life contexts. Before solving, check both the formula and the unit so you do not mix systems or scales.
Define the core 2D shapes first
The shape tells you which lengths matter in the calculation.
Define the shape before you decide which formula fits.
Perimeter adds the boundary
A rectangle with sides 7 cm and 4 cm has perimeter 7 + 4 + 7 + 4.
Perimeter is measured in ordinary units such as centimetres.
Area formulas depend on the shape
A triangle is half of a matching rectangle, while a parallelogram uses base times perpendicular height.
| Shape | Formula idea | Example |
|---|---|---|
| Rectangle | length x width | 6 x 3 = 18 cm^2 |
| Triangle | 1/2 x base x height | 1/2 x 8 x 5 = 20 cm^2 |
| Parallelogram | base x perpendicular height | 9 x 4 = 36 cm^2 |
Area is measured in square units, not plain centimetres.
Metric and imperial units
Choose the unit system that matches the context, then keep it consistent.
mm, cm, m, km; g, kg; ml, l
Common in school maths and linked by powers of 10
in, ft, yd, miles; oz, lb; pints, gallons
Still seen in road distances, height and some everyday measures
Do not mix unit systems in one calculation unless you convert first.
Key measurement conversions
Some questions need a quick conversion before you calculate perimeter or area.
| Metric conversions | Imperial conversions |
|---|---|
| 10 mm = 1 cm | 12 in = 1 ft |
| 100 cm = 1 m | 3 ft = 1 yd |
| 1000 m = 1 km | 1760 yd = 1 mile |
Convert first, then calculate, so every length is in one unit.
Find the area of a parallelogram with base 9 cm and perpendicular height 4 cm.
| Base | Height | Area |
|---|---|---|
| 9 cm | 4 cm | 36 cm^2 |
Decide first whether the problem asks for perimeter or area, then choose the correct unit.
What is the perimeter of a rectangle with length 7 cm and width 4 cm?
What is the area of a rectangle with length 6 cm and width 3 cm?
What is the area of a triangle with base 8 cm and height 5 cm?
Which conversion is correct?
| Remember |
|---|
| 10 mm = 1 cm |
| 100 cm = 1 m |
| 1000 m = 1 km |
Which statement is correct?
| Measure | What it describes |
|---|---|
| Perimeter | boundary |
| Area | space inside |
Watch for these when working through the lesson.
These ideas fit closely with this lesson.