Area of common shapes and circles

Area measures the space inside a flat shape, in square units (cm², m², …). Perimeter is the distance around the outside.

• Rectangle: $A = l \times w$
• Triangle: $A = \tfrac{1}{2} b h$ — half of a rectangle with the same base and height
• Parallelogram: $A = b h$ (use the perpendicular height, not the slanted side)
• Trapezium: $A = \tfrac{1}{2}(a + b)h$

Circles