To substitute 1 teaspoon baking powder, use ¼ teaspoon baking soda plus ½ teaspoon cream of tartar.
To convert a recipe from all-purpose flour to cake flour use 1 cup and 2 tablespoons of cake flour for each cup of all-purpose flour.
To use cake flour in a recipe that calls for self-rising cake flour use 1 cup cake flour, ½ teaspoon baking powder and ¼ teaspoon salt.