Make sure that all those figures are in feet and you'll get the answer by multiplying all of them. The only figure that is not in feet is 5". But 5" = 5/12' Now it is simple. The volume is (all dimensions are in [ft] so the volume is in cubic feet): 7 * 3 * 5/12 = 7 * 5 / 4 = 35/4 = 8.75 ...