Thank you for reaching out to Ask Betty with your inquiry! I have a recipe that uses a 13"x9" pan. I will list it below for your convenience. Happy baking!

YOU WILL NEED                1 1/4 CUPS WATER

1.  MOVE oven rack to middle position.  HEAT oven to 350°--metal or glass pan. 

2.  BEAT cake mix and water in large (4-quart) glass or metal bowl on low speed 30 seconds; scrape side of bowl.  Beat on medium speed 1 minute.  Pour intoungreased pan. 

3.  SPREAD batter evenly in rectangular pan.  

4.  BAKE 13"x9"x2" rectangular pan 35-45 min until cracks feel dry and crust is dark golden brown..  

5.  COOL rectangular pan upside down, resting each corner on can of equal height.