I think you want to ask, the volume of cube of 3 cm :)
So, the answer for that is
Volume of cube = s³
Why ?
Now, since area of square is s², we can see that many squares are placed over each other to form this cube.So, how many squares are placed - s
That's why its volume is s³
Volume = (3)³ = 3 × 3 × 3 = 27 cm³