The perimeter of a shape is the distance around its edges--the distance you
would have to travel to walk once around the shape along its edge. In general,
the perimeter of a shape is the sum of the lengths of its sides.

Perimeter of a Polygon

A polygon is a closed shape made up of several straight line segments. The
perimeter of a polygon is the sum of the length of all these sides. For
example, the perimeter of the polygon pictured below is equal to
1 + 5 + 4 + 2 + 7 = 19:

Perimeter of a Rectangle

A rectangle is a 4-sided polygon in which opposite sides have the same
length and all angles have the same measure. Since opposite sides have the same
length, we have only to add the lengths of two adjacent sides and
multiply by 2 (so each side is "counted" twice). The formula for the perimeter
of a rectangle is 2×(h + w), where h and w are
the height and width of the rectangle. For example, the perimeter of the
rectangle below is 2×(3 + 6) = 2×9 = 18.

Perimeter of a Square

A square is a 4-sided polygon in which all the sides are the same length.
Therefore, to find the perimeter of a square, we have only to multiply one side
by 4. The formula for the area of a square is 4×s, where s
is the length of a side. For example, the perimeter of the square below is
4×8 = 32: