A fat quarter of a yard is a fat quarter, period. If the fabric is only 36 inches wide, then a quarter of a yard will be 9 inches long by 36 inches wide. It stands to reason then, that a fat quarter is only going to be 18 inches wide by 18 inches long. There is no written rule that a fat quarter has to be 18 by 21 or 22. It is that because the width of the fabric is 42 or 44 inches.