For my culinary school cake decorating classes we used a cake mix for each 9 inch layer and then trimmed the cake layer using the top of the cake pan as a guide. Then we torted and filled each layer--making a four layer cake. Our cakes were required to be at least 4 inches high or they were marked down. I haven't used the cake extender recipes yet. Also, Wilton has a chart with how much batter each size cake layer takes. It is a chart on their website.

I hope that helps.

Lera

Thanks for sharing that info with us!