Area and Perimeter
- Formula / Rule
- Area and Perimeter
- Topic
- Geometry
- Formula
Shape Area Perimeter Rectangle $l \times b$ $2(l + b)$ Square $a^2$ $4a$ Triangle $\frac{1}{2} \times b \times h$ $a + b + c$ Circle $\pi r^2$ $2\pi r$ Parallelogram $b \times h$ $2(a + b)$ Trapezium $\frac{1}{2}(a+b)h$ $a+b+c+d$ Heron's Formula (for a triangle with sides $a, b, c$): $A = \sqrt{s(s-a)(s-b)(s-c)}$, where $s = \frac{a+b+c}{2}$
- When to Use
- Finding the area or perimeter/circumference of 2D shapes.
- Worked Example
Q: Find the area of a circle with radius $7 \text{ cm}$.
$\text{Area} = \pi r^2 = \frac{22}{7} \times 7^2 = \frac{22}{7} \times 49 = 22 \times 7 = 154 \text{ cm}^2$