According to J&O Fabrics, the average amount of fabric needed to make a queen-size quilt is around 14 yards. A quilt of this size covers a queen bed, but it might not reach the floor depending on the size of the box spring and bed frame.
About.com points out that it is also important for quilt makers to think about what style of binding they plan to use when finishing the quilt. Binding helps to protect the quilt fabric from fraying. The style of binding that is chosen for a quilt affects the amount of fabric that is needed in the overall quilt.