What Is Perimeter?
Perimeter is the total length of the boundary around a flat (two-dimensional) shape — add up the lengths of every side. For a circle, the equivalent measurement is called the circumference instead, calculated differently since a circle has no straight sides.
Example
A rectangle with a length of 8 and a width of 5 has a perimeter of 2(8) + 2(5) = 16 + 10 = 26.