Square yards and cubic yards are measurements in different dimensions, and are therefore incompatible. One is a measure of area and the other of volume. The volume is 5.5*6*3=99 cubic feet=99/27=11/3=3.67 cubic yards. Builders' merchants may quote fill in square yards because the depth of fill is standardised. To find out how much you need, you will need to know this depth. Let's put a value on this as an example, and take the depth as one foot, or 1/3 of a yard. So the amount of 1-ft fill in square yards you need is 11/3 divided by 1/3, which is the same as multiplying by 3, so you would need sufficient for 11 square yards to fill 3.67 cubic yards. If the depth of fill is only 6 inches (1/6 yard), you would need twice as much: 11/3*6=22 square yards. If the quoted depth of fill is 3 feet (1 yard), you would need only 3.67 square yards.
