What exponents do you know that share names with different kinds of shapes? It may surprise you (or not) to discover that taking the square of a number and taking the cube of a number both derive their names from finding the space inside a square and a cube respectively. For squaring (as in x²) this corresponds to calculating the area of a square with side lengths x. For cubing (as in x³), it corresponds to calculating the volume of a cube with edge lengths x.
So, if we want to find the volume of a cube with edge length 5 in, we just need to find the value of 5³. (Keep in mind that our final units will be in in³)