Do you use the same amount of cake flour as all purpose flour in a recipe?

No. If the recipe calls for all purpose flour and you want to use cake flour, add an additional 2 tablespoons cake flour per each cup called for in the recipe. If the recipe calls for cake flour and you want to use all purpose flour, then you do the opposite - use 1 cup all purpose flour minus 2 tablespoons per cup.

But if using all purpose flour when the recipe calls for cake flour, be sure to sift it. Cake flour is lighter and more airy than all purpose flour.