I am making a sheet cake for a bar mitzvah (with a decoration on top, but the base is a sheet cake)

The cake is for 100 people. how big does the cake need to be?
I have a 12x18x2 pan. So how would i have to arrange the cakes?
also any tips on covering such a large cake with fondant?

2 of that size pan cakes put side by side is a full sheet cake and it willl give you 108 servings of cake

What size servings did the customer request or which do you normally provide: 1x1x4 or 1-1/2x2x4 or 2x2 or 2x3.

You don't have to abutt the sheet cakes, you could stack them - either way would yield the same amount of servings.

Cake preparation and servings guides:
(Gives batter requirements by pan size, as well as wedding or party servings.)

http://www.wilton.com/cakes/making-cakes/

Illustrated guide by indydebi on cutting neat slices of tiered cake:

http://cateritsimple.com/_wsn/page10.html

How to determine servings of single layer sheet cakes:
(Also by indydebi.)

http://forum.cakecentral.com/cake-decorating-ftopict-302303-.html

I would recommend the WASC cake as it makes a tad over 14 cups of batter (using DH white cake mixes) which is the required amount for a 12x18x2 pan.

Here's the expanded flavors version of the WASC recipe:

http://tinyurl.com/2cu8s4

HTH

What size servings did the customer request or which do you normally provide: 1x1x4 or 1-1/2x2x4 or 2x2 or 2x3.

You don't have to abutt the sheet cakes, you could stack them - either way would yield the same amount of servings.

Cake preparation and servings guides:
(Gives batter requirements by pan size, as well as wedding or party servings.)

http://www.wilton.com/cakes/making-cakes/

Illustrated guide by indydebi on cutting neat slices of tiered cake:

http://cateritsimple.com/_wsn/page10.html

How to determine servings of single layer sheet cakes:
(Also by indydebi.)

http://forum.cakecentral.com/cake-decorating-ftopict-302303-.html

I would recommend the WASC cake as it makes a tad over 14 cups of batter (using DH white cake mixes) which is the required amount for a 12x18x2 pan.

Here's the expanded flavors version of the WASC recipe:

http://tinyurl.com/2cu8s4

HTH

Thanks KHalested!

JanH, thanks for all the useful links. The customer wants a chocolate cake, and I have a great recipe that I have to figure out how to triple or quadruple. Plus it can't be dairy at all!
I'm so bad at that, usually i just make each single recipe then combine!

Sorry about the double post.

Also, there's a typo - a wedding serving size is 1x2x4 (not 1x1x4).