The perimeter of a 4-foot square is 16 feet. To determine the perimeter, add each of the four sides together.
All four sides of a square are equal, so in the case of a 4-foot square, the problem would be written out as 4+4+4+4=16. The formula is also the same for calculating the perimeter of a rectangle, with the main difference being two sides of a rectangle are longer. So, for example, if a rectangle was 4 feet by 6 feet, its perimeter would be 20 feet. The problem would be written as 4+4+6+6=20. To calculate the perimeter of any polygon, measure the length of each outer line, and add the numbers together to determine the perimeter.