Definition:
The total distance around the outside of a
polygon

Try this
Drag any orange dot to resize the polygon. The perimeter is calculated as you drag.

How to find the perimeter of a polygon

The perimeter of any polygon is the total distance around the outside,
which can be found by adding together the length of each side.
For example, a quadrilateral whose sides are 12,6,9 and 8, the perimeter is the sum of these, or:

Perimeter = 12+6+9+8 = 35

Regular Polygons

For regular polygons, where all the sides are the same length, the perimeter is n times the length of any side,
where n is the number of sides. Or as a formula:

perimeter = ns

where: n is the number of sides s is the length of any side

In the figure above, drag any orange dot to resize the polygon. Adjust the number of sides and choose regular or irregular.
From side lengths shown, calculate the perimeter
and verify your result matches the display in the diagram.