Area & Perimeter of 2D Shapes

Perimeter is the total distance around a shape (a length, in cm or m). Area is the space inside it (in square units, cm² or m²).

• Rectangle: area $= l \times w$, perimeter $= 2(l + w)$.
• Triangle: area $= \tfrac{1}{2} \times b \times h$.
• Circle: area $= \pi r^2$, circumference $= 2\pi r$.

For circle calculations at this level, use $\pi \approx \dfrac{22}{7}$ or $3.14$. The radius $r$ is the distance from the centre to the edge.

Worked example. A rectangle is $8$ cm by $5$ cm. Area $= 8 \times 5 = 40$ cm². Perimeter $= 2(8 + 5) = 26$ cm.