Area | COSMOS

The term ‘area’ is a quantity giving the size of a two-dimensional region or shape within a given enclosed border.

The formulae for the area $A$ of common shapes are:

shape	formula	note
square	$A = a^2$	where $a$ is the length of one of the sides
rectangle	$A = ab$	where $a$ is the base and $b$ is the height
circle	$A$ = $\pi r^2$	where $r$ is the radius
triangle	$A = 0.5ab$	where $a$ is the base and $b$ is the height