Shane,
Since you want the volume in cubic yards, (yards yards yards) you need all three dimensions in yards. There are 3 feet in a yard and 36 inches in a yard and hence
4 inches is ^{4}/_{36} yards
18 feet is ^{18}/_{3} yards and
27 feet is ^{27}/_{3} yards
Thus the volume is
^{4}/_{36} ^{18}/_{3} ^{27}/_{3} = 6 cubic yards.
Penny
