The ratio of the side length of a square to the square's perimeter is always 1 to 4. Peter drew a square with a perimeter of 28 inches.
What is the side length of the square Peter drew?
Let's say the side length of the square Peter drew is x inches.
The perimeter of the square is given by 4 times the side length, so 4x = 28 inches.
Dividing both sides of the equation by 4, we get x = 7 inches.
Therefore, the side length of the square Peter drew is 7 inches. Answer: \boxed{7}.