By definition, a square is a two-dimensional figure containing two sets of parallel sides with equal measures of length. So, when we talk about square, we only have one information about it: the side length. The area of the square is the square of the side length. So, if the area is 18 square meters,
A = s²
18 = s²
s = √18
s = 3√2 or 4.24 meters