A square inch is simply 1 inch x 1 inch, or 1' x 1'. It is used to mark the area. Usually when the length and the width of a rectangular or a square are given, we multiply both (L x W) to find the area which is in square inches.
For example if the length of a rectangle is 5 inches, and the width is 5 inches as well, the area becomes 25 square inches.
For example if the length of a rectangle is 5 inches, and the width is 5 inches as well, the area becomes 25 square inches.