To find the volume of a cube (or box) with equal side lengths, you can use the formula:
\[ \text{Volume} = \text{side}^3 \]
In this case, the side length is 20 inches.
\[ \text{Volume} = 20 , \text{inches} \times 20 , \text{inches} \times 20 , \text{inches} = 20^3 = 8000 , \text{cubic inches} \]
So, the volume of the large box is 8000 cubic inches.