How many boxes of cake mix needed for a 12 x 18 cake pan?

For a 12 x 18-inch cake pan, you typically need about 3 boxes of cake mix. Each standard box of cake mix usually makes about 12 cups of batter, and a 12 x 18 pan generally requires around 18 cups of batter. It's always a good idea to check the specific instructions on the cake mix box for any variations.