I am making a "from scratch" carrot cake for a friend.  I am putting it into a 12x18 sheet pan.  I am wondering how many recipes of the cake I should make to fill the pan.  I'd like the cake about 2" high. Heres the recipe:

In general one fills a pan 1/2 to 3/2rds full.  That sounds like a typical recipe yielding about the same as one cake mix so I'd say you need 3 to 3 1/2 batches.

That is going to be a very moist heavy cake.  Be careful trying to remove it from the pan.  Be sure to prep the pan well and after it has cooled about 10 minutes out of the oven, put a cake rack over the pan & turn the whole thing over together.  The cake should fall out b y itself.  If it doesn't, flip again, remove the rack and run a spatula/knife around the edges lifting the corners to loosen the cake and try again.   If you try lifting the cake out it most likely will break :(

I do NOT like measuring by the cupful as most people don't scrape the cup properly so the amount is not exact and it is soooooo very messy.  Why bother when you can do it another way that is less messy?

oh thank you so much for your help

AWilton has a chart for that. http://www.wilton.com/cakes/making-cakes/baking-party-cake-2-inch-pans.cfm

I agree with kakeladi though. I never measure my batter out by the cupful.

The one response I read was very true-- you are going to have a lot of trouble getting that cake out of the pan without it breaking, and if you try to torte or layer it -- watch out.  I just did a carrot cake that serves 30 comfortably using 10" round pans.  I made two recipes and divided them between 4 10" round pans (parchment on bottom please)-- I had to do two bakings.  The layers were thin so baking time was only 15 minutes.  I also made 2 recipes of the cream cheese frosting as filling and icing.  I then had 4 layers and the cake was about 4 inches tall, but very easy to remove from the pan, cool, and handle.  The reviews were amazing.

I have generally found that if a cake recipe makes two 8 or 9-inch layers, it is enough for one half sheet pan.  

7 cups for 2 8" pans, and 14 cups for a 12x18 half sheet pan.

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