How many serving would a 2 layer 1/2 sheet feed and how much would a single layer 1/2 sheet feed. How about a 12 x 18 is that considered a 1/2 sheet or a full sheet

Forget sheet, half sheet - we can't agree what these terms mean...

Instead ask your customer how many servings they need. (And are your servings 1x2x4 or 1-1/2x2x4 which is the same as 2x2x2 or 3x2x2.

If your customer wants to serve larger portions, they will need to order MORE servings.

If you include indydebi's cake cutting guide the cake serving yield will be the same or slighter more than Wilton's:

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

Everything you need to know to make, decorate and assemble tiered/stacked/layer cakes:

http://www.cakecentral.com/cake-decorating-ftopict-605188-.html

Above thread has links to all four Wilton cake preparation and servings guides and SO much more.

HTH

Thanks for all the info. I'll take that into account. What is the servings difference between a single layer and a double layer half sheet. Or an estimate.

12x18 single layer should yield 54 2x2 servings or 36 2x3 servings (12x18 is considered among other close sizes to be 1/2 sheet...) so a double layer should yield you twice that many servings only they'd be cut 1x2 or 1.5x2.

Oh and I found this thread that might answer some of your other questions...

http://www.cakecentral.com/cake-decorating-ftopict-615309-heights.html

HTH