The area of a square is given by the formula:
\[ \text{Area} = \text{side length}^2 \]
If the area is 64, we can set up the equation:
\[ \text{side length}^2 = 64 \]
To find the length of each side, we take the square root of both sides:
\[ \text{side length} = \sqrt{64} \]
Calculating the square root gives us:
\[ \text{side length} = 8 \]
Therefore, the length of each side of the square is 8 units.