I repeatedly have people needing to have just one layer (2" tall) cakes in round pans and square. Is there somewhere I can find a chart that tells how many party servings would be in a 16" square one layer cake for example? Is it as simple as dividing the wilton 2-layer cake serving chart by two?

I think so. People may cut larger slices of one layer since it looks smaller on the plate, but if they are using the cutting guide they should be fine. Just make sure they know what size a 'serving' is when they order.

Logically, a serving of a single layer would be twice the area of a serving from a double layer-- that would pretty much keep the volume of the piece consistent from single to double layer cakes. On the Wilton site they give portions and say:

"The serving amounts listed are based on party-sized portions of approximately 1-1/2 x 2 inches or wedding-sized portions which are cut smaller, about 1 x 2 inches. Cakes from 3 to 6 in. high, baked in the same size pan, would yield the same number of servings because they follow the same pattern of cutting. Cakes shorter than 3 in. would yield half the number of servings indicated for that pan. "

http://www.wilton.com/cake/cakeprep/baking/times/index.cfm

So I guess, whether you use the Wilton serving number, Earlene's, or some other count, the number of single layer servings would be half of a double-layer cake of from the same pan size.

Well, that makes sense. It seemed too easy, so I figured I was thinking of it wrong. Thanks for your help!