The magnitude of the rotational symmetry in a square is 4.
The rotational symmetry of a geometric figure is the number of times you can rotate the geometric figure so that it looks exactly the same as the original figure.
So when we roll up a square and stopped when every side is at the bottom, the square is still congruent to its original figure. Since a square has 4 sides, we can roll it up 4 times, every 90 degrees rotation.
