Perimeter is the distance around a shape; area is the space inside it.
Formulae
Rectangle: area $= l \times w$, perimeter $= 2(l + w)$.
Triangle: area $= \tfrac12 \times \text{base} \times \text{height}$.
Example: a $5 \times 3$ rectangle has area $15$ and perimeter $16$. A triangle with base 6 and height 4 has area $\tfrac12 \times 6 \times 4 = 12$.
Remember
- Area is in square units; perimeter is a length.
- Triangle area $= \tfrac12 bh$.