I am new to decorating and I was needing to find out how many serving are in the 11x15 pan from Wilton?
I usually tell my clients that a single layer 11x15 sheet pan will feed around 30-35 people depending how big they cut the slices. I also think the insert in the pan will tell you how many people it will feed.
here is a link from wilton that you might find helpful. Scroll down on the page and there will be a chart with pan sizes and serving amounts.
here's another one from Earlene's
These charts are just guides though, because, like Traci said, it all depends on how large they cut their pieces.
I do the 11x15 pan as two layers of cake and one layer of filling and tell my customers that it will feed approximately 35 people. I personally have gotten 40 servings from this cake size (filled).