Is this a 1/2 sheet pan? I found it in my pans & thought I might try baking a cake in this to practice decorating on. It will give me lots of room to practice on. Also, I use boxed cake mixes, no doctoring, so does anybody know how many cake mixes it will take? Sorry for the long & dumb question but I could not find anything on google. Thanks for any info you can give me.

the industry standard for a half sheet cake is 18"x12". I know that there is a slight variation in size if you are baking a true full sheet and then trimming the sides and cutting it down, and i knwo someone posted that info somewhere on this site but can't find it right now.

How many cake mixes it takes will really depend on the brand and flavor of cake mix you are using. Depending on the brand they yield anywhere from 3-5 cups. And even in the same brand different flavors yield different amounts - but from flavor to flavor it's typically within 1/2 cup.

here is the wilton chart that states how many cups you need for each 2" tall pan. Once you know how many cups one of your box mixes makes then you can figure out how many boxes you need.

http://www.wilton.com/cakes/making-cakes/baking-wedding-cake-2-inch-pans.cfm

I have a 12x18 pan so when i use DH white or chocolate i find that it makes just about 5 cups per box mix so i would need 3 boxes. But if you make a Pilsbury that yields closer to 3 cups then you'll need 4.5 boxes