if substituing cake flour for all-purpose flour do i use the same amount

To substitute cake flour for all-purpose flour use 1 cup plus 2 tablespoons cake flour for every cup of all-purpose flour. Make your own - one cup sifted cake flour (100 grams) can be substituted with 3/4 cup (85 grams) sifted bleached all-purpose flour plus 2 tablespoons (15 grams) cornstarch.

SOURCE: http://www.joyofbaking.com/flour.html