What square? I must assume you mean any of the 6 sides of the cube.
Volume of a cube of side length s is V = s^3. Thus, 12.167 in^3 = s^3, and s = 2.3 in.
The length of one side of the cube is 2.3 in. Equivalently, the length of one side of the square base of the cube is 2.3 in.