The side of the square whose perimeter is 20 m will be___________m.

Given, perimeter of square = 20 m

As we know, the perimeter of square = 4 x side length

So, 

20 = 4 x side length

Side length = $\frac{20}{4}$

Side length = 5 m

Therefore, the side length of the square is 5 m.