That certainly is not enough for a king.I make king all the time and you need 10 yards of 42 in. fabric for a king back.You also need to tell the lady that the quilting pulls in the fabric in the back so depending on the loft of the batting you need the back to be at least 6 in. longer and wider than the front.This is a thing the inexperienced clerk did not know.If the loft of the batting is deep the backing must be bigger than the 6 in.