I am attempting to convert the Downy yellow butter cake into a 11 X 15 X 2 inch sheet cake. I have read and re-read the Cake Bible and the conversion charts but it just doesn’t make sense to me. Rose says for a cake of that size that you should use Level 5 because the width is closest to 18 inches. I am so new to this and understand that the amount of baking powder needs to be decreased the larger the pan. However, if I multiply the base by 17 as the rose factor suggests, I come up with almost 15 teaspoons of baking powder. Is that correct? Or am I just really not understanding this. Also, is there anything else that I need to multiply by the rose factor, or can I just double the remainder of the recipe? I need urgent help with this, my daughters birthday is this weekend and I do not want to have to bake a practice sheet cake. If anyone has tried to convert this cake and it has worked for you, could you give me specifics that will help wih some of the guess work?