It calls for a 9 oz. package of yellow cake mix, but of course all I had was the standard 18.25 oz. box, so I measured 9 oz. with my digital scale. I didn't think to measure out how many cups it was. I'm guessing it would be just over 1 cup, like maybe 1 cup plus 1 Tbs. or maybe 2 Tbs. The recipe makes about 14 muffins, which is annoying. You'll have to dirty another muffin tin, only bake 12 muffins and discard the rest of the batter, or bake 2 muffins after the first 12 are done if you only have one tin.
1/2 c. water
1/3 c. milk
2 Tbs. vegetable oil
9 oz. yellow cake mix
1 (8.5 oz.) package cornbread mix
In a bowl, combine the eggs, water, milk, and oil. Stir in mixes and mix well. Grease and flour muffin cups (take my advice and buy the cooking spray for baking that has flour in it). Fill muffin cups half full. Bake at 350 degrees for 18-22 minutes or until a toothpick inserted in center of muffin comes out clean. Cool for 5 minutes before removing from pan.