Perimeter

The perimeter of a polygon (or any other closed curve, such as a circle) is the distance around the outside.

Here are some formulas for the perimeters of common plane figures.

Perimeter Formulas
Shape	Formula	Variables
Square	$P = 4 s$	$s$ is the length of the side of the square.
Rectangle	$P = 2 L + 2 W$	$L$ and $W$ are the lengths of the rectangle's sides (length and width).
Triangle	$a + b + c$	$a, b$ , and $c$ are the side lengths.
Right Triangle, with legs $a$ and $b$ (see Pythagorean Theorem )	$P = a + b + \sqrt{a^{2} + b^{2}}$	$a$ and $b$ are the lengths of the two legs of the triangle
Circle	$P = C = 2 π r = π d$	$r$ is the radius and $d$ is the diameter.