Perimeter and Area

Perimeter is the distance around the edge of a shape (a length, so metres). Area is the amount of surface it covers (measured in square units, like $\text{m}^2$).

Key formulas:

• Rectangle: area $= l \times b$, perimeter $= 2(l + b)$.
• Square: area $= s \times s = s^2$, perimeter $= 4s$.
• Triangle: area $= \dfrac{1}{2} \times \text{base} \times \text{height}$.

Worked example. A rectangle $12\,\text{m}$ by $5\,\text{m}$: area $= 12 \times 5 = 60\,\text{m}^2$; perimeter $= 2(12 + 5) = 34\,\text{m}$.

Exam checkpoint

Perimeter measures the distance around a shape; area measures the surface inside it. Write units correctly: perimeter uses units such as cm, while area uses square units such as $\text{cm}^2$. For a rectangle, add all sides for perimeter and multiply length by width for area.

Short worked example. A rectangle is 8 cm by 5 cm. Perimeter $=8+5+8+5=26$ cm. Area $=8\times5=40\text{ cm}^2$.