Robyn - from Houston, TX
For the cake to bake up and completely fill a 9 x 13 sheet cake pan, you will need to use 7 cups of cake batter. Most mixes make only about 5 cups batter. To make enough to fill your pan, I suggest you make up two boxes of mix, then measure 7 cups batter into the pan. Use the leftover to make smaller cake layers or cupcakes – they can be frozen for use at a later time!