I think 1 will do. 2 if you want a really big, puffy cake, but it might overflow. I always make cakes from scratch. They taste much better. I hate box cakes. People who use box recipes are lazy. Just get a cookbook. ;-)
2 boxes of cake mix
There are 11 cups of batter in an 11x15 pan for a 2 inch layer. I would guess for an 11x13, maybe 10 cups?
It depends on the depth of the pan
It depends on how deep the pan is.
One can purchase cake boxes wholesale from many different locations. However one can purchase cake boxes from locations such as Sam's Club, Target, Kohls, Walmart and TheCustomBoxes.com.au.
You can buy cup cake boxes from online retailers at websites such as: www.brpboxshop.com, www.papermart.com, and www.wilton.com. You can also buy cup cake boxes in store at Michael's and Walmart.
You can find cake boxes at any of these links: http://www.michaels.com/Cake-Boxes/products-bakeware-packaging-cakeboxes,default,sc.html, www.brpboxshop.com/cake-boxes.html, or http://www.papermart.com/Product%20Pages/Product.aspx?GroupID=18883.
4 boxes for a single pan
You can actually use one box alone but it will be thinner. you can actually use the amount of boxes of cake mix you want it will just get thicker.
Oriental Trading is an online site that sells cake boxes for wedding cake. These boxes are high quality and will meet the needs of the bride and groom. It is very important that the box that is used to transport the wedding cake is sturdy and has a freezer safe plastic bag for storage.
Large square boxes, the cake is often separated into separate boxes. Another common box is a very large box with a whole cake enclosed in it, these are less common due to the size of wedding cakes.
For more information on great cake boxes of wholesalers kindly check the provided links. http://www.cakeboxeswholesale.org/ http://www.boxandwrap.com/pastrybox.html http://www.mrtakeoutbags.com/store/round-cake-boxes.html
Check out the website brpboxshop.com. This website is devoted to food boxes. Cake boxes that are original and eye-catching would never be considered common and would still be a great business tool.