The boxes I checked said one box would make a 13x9, so you will need about 1 1/2 boxes for a 12x18. Assuming the pan is deep enough you could use two boxes for a one layer 12x18 or you may want to make a two layer cake using 1 1/2 box per layer.
It depends on how deep the pan is.
It depends on the depth of the pan
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.
The number of boxes of cake mix needed depends on the size of your cake pans. Generally, one box of cake mix makes about 4 to 5 cups of batter, which is sufficient for a 9-inch round or square pan. For larger pans, such as 12-inch or 10-inch rounds, you may need 2 boxes, while for a 9x13-inch pan, one box is usually adequate. Always check the specific instructions on the cake mix box for the best results.
About 2 boxed cake mixes.
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.
There are 11 cups of batter in an 11x15 pan for a 2 inch layer. I would guess for an 11x13, maybe 10 cups?
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. ;-)
yes, it wont be that tall but it will work ok.
Generally it depends on how deep (how many layers) your cake is. Standard serving size of a piece of cake is 1" x 2". Also depending on how large you want to cut your slices (sensible vs generous), a 7" round cake can serve anywhere from 6-10 people.
I know this sounds crazy .... look on the back of the box and triple it.