To find the volume of a pyramid, we can use the formula: V = (1/3) * B * h, where V is the volume, B is the area of the base, and h is the height.
The area of the rectangular base is length * width = 8 inches * 12 inches = 96 square inches.
The volume of the pyramid is (1/3) * 96 square inches * 20 inches = 1,920 cubic inches. Answer: \boxed{1920}.