Note that when measuring flour by volume it should always be freshly sifted flour. So that "one cup flour" really means "one cup sifted flour. Sift onto a separate surface, such as a sheet of waxed paper, and then lightly transfer (without packing) into the cup measure, and level off the top with a knife or spatula.

If you don't sift, or pack the flour in the cup measure, you will have too much flour, and can get disastrous consequences.

Dave Oesterreich