wikiHow Square Perimeter Calculator To calculate the perimeter of a square, you need to know the length of one side. The perimeter of any polygon is the sum of the lengths of all its sides. In the case of a square, all four sides have equal length. The formula to calculate the perimeter of a square is: Perimeter = 4 x side Here, "side" refers to the length of one side of the square. For example, if you have a square with a side length of 5 units, the perimeter would be: Perimeter = 4 x 5 = 20 units So, the perimeter of the square is 20 units. Page